The elder of the Lopez-Fitzgerald daughters, Theresa has been the apple of not only her mother's but her brothers' eyes as well. After her father disappeared when she was three, she was raised primarily by her older brother Antonio, as her mother worked two jobs to support them. Antonio disappeared when she was thirteen, and Luis took over as her surrogate father. When she was a teenager, Theresa began cutting photographs of Ethan Crane out of magazines and putting them on her walls, convinced that one day Ethan would come to Harmony, fall in love with her, and she would live happily ever after in the Crane mansion. Her belief in this was so strong that she refused every date she was asked out, saving herself for Ethan, whom at that time she had never met. Theresa thought her dreams were finally coming true when Ethan came to town the summer before her senior year. The only drawback was that he brought his long-time girlfriend Gwen Hotchkiss with him, a woman Theresa had never met, but had disliked for years because she was with Ethan. Theresa was nervous around Ethan, and a number of rather smelly accidents ensued. Theresa was convinced that if she could just get Ethan alone she could explain everything, but when she snuck into his room, she ended up overhearing him tell Gwen that people like her were just gold-diggers, and hearing Gwen try to defend her. That didn't dissuade her in her plans to have a future with Ethan...when Ivy offered her a job as her social secretary, she soon accepted, thinking it would be the perfect way to get close to Ethan so that he would realize they belonged together.
When Ethan realized Theresa was the girl who was dropping smelly sauces on him, he planned to have her arrested and charged with stalking, but Whitney explained that Theresa was just nervous around him, and they denied that Theresa had any romantic interest in Ethan. When Ethan assumed that Theresa had a boyfriend she let him believe it, knowing that Gwen was suspicious of her, and that if Ethan and Gwen knew she didn't have a boyfriend, they wouldn't let her spend time with them, particularly Ethan. Theresa was thrilled when Julian asked her to deliver some papers to Ethan up at the Crane cabin, and she told the driver to leave after he dropped her off so she could spend time alone with Ethan. It didn't last long, though, because Gwen soon showed up for the romantic weekend she and Gwen had planned. Gwen was getting more and more suspicious, and demanded that Theresa produce her boyfriend. Theresa planned to meet them at the Seascape, and spent her life's savings on a dress to impress Ethan. Her plan was to trip a waiter and have him drop soup on Gwen, have her go ballistic, and Ethan would realize she [Theresa] was the woman for him, and there would be no need to produce a boyfriend. Unfortunately, Gwen was extremely gracious. Theresa was saved when Whitney had a friend pose as her boyfriend, Chuck. Gwen apologized for her suspicions, and Ethan apologized for attacking Theresa moments earlier and accusing her of lying to get close to him.
Theresa began to despair of Ethan ever realising that they were meant for each other, especially once she found out that Ethan planned to ask Gwen to marry him! He took Theresa with him to help him pick a ring for Gwen, and when the ring was stuck on Theresa's finger, she believed it was fate. The ring was stuck for days, and when Gwen caught a glimpse of it and asked about it, Theresa told her that she and Chuck were engaged to be married. The whole group of them ended up at the lake on Valentine's Day, where Theresa toyed with showing Gwen the ring, wanting to speed up her future with Ethan. Whitney had to stop her from flashing the ring, and before she could do it again, she learned that Charity had fallen through the ice. Charity was rescued, but then Miguel fell in. Theresa was a vital part in her brother's rescue, and vowed to God that she would stop coming between Ethan and Gwen unless Ethan made it clear that he wanted her. That night, when Ethan phoned her to ask if the ring had come off yet so he could give it to his new fiancée Gwen, Theresa lied to him. Even though the ring was off, she said it was still stuck. She went to the mansion the next day because she was convinced that by now Ethan and Gwen would be finished and she and Ethan could start their life together, but when she saw how deeply in love with Gwen he was, and how it was hurting him to think of losing her, she took the ring off her finger and gave it to him. Gwen was ecstatic, but Theresa was heartbroken.
Theresa's pain was so intense she couldn't hide it from those around her. It was only a matter of time before Gwen wanted to know what was going on, and Theresa told her that Chuck had dumped her because of her family's financial status. When Ethan and Gwen asked her to plan their wedding, she put up a small protest, but soon took the job. As she told Whitney, being their wedding planner and pretending to be Gwen's friend would be the perfect way to show Ethan that they were meant to be together. While Gwen was out of town, Theresa and Ethan took a trip to Bermuda to check out a resort for Gwen and Ethan's honeymoon. When she got home and Luis saw all the expensive clothes Ethan had bought for her in Bermuda, he was furious, until he decided they were probably just hand-me-downs from the Cranes two daughters. Theresa thought that she had finally shown Ethan that they were meant to be together, but he continued his plans to wed Gwen. She finally confessed that she loved him aboard the prom boat, but Ethan wouldn't listen to her. He told her she was just on the rebound after what Chuck did to her. When Gwen asked her later, Theresa lied to Gwen and told her that she had no interest in Ethan at all. But she couldn't stop thinking about Ethan, and when he told her there was no chance for them, she hopped on Miguel's motorcycle and took off. She was driving in the on-coming traffic lane when she realized the brakes were out, and nearly had a head-on collision with a trucker.
Theresa woke up in the hospital to Ethan telling her he loved her, and the two of them sharing their first real kiss. Theresa begins to believe the two of them will share a future together, until Ethan tells her it's not quite that simple...he still loves Gwen. When Rebecca attacks Theresa, Gwen defends her, convinced that her friend would never hurt her like that. This goes on for months, Rebecca attacking Theresa, Gwen defending Theresa, and Theresa and Ethan taking advantage of every stolen moment, until the eve of Gwen and Ethan's wedding. Rebecca told Theresa that Ethan was just using her, and a heart-broken Theresa went back home, planning to leave town. While pulling a suitcase out of the closet, another suitcase fell, this one containing Ivy's letter to Sam about Ethan's paternity! Theresa was shocked to learn that Ethan was a Bennett, and immediately scanned the documents into the laptop she used for her work as Ivy's secretary. She planned to take the information to Ivy so that Ivy would make Ethan break up with Gwen and marry her. She changed her mind, deciding instead to tell Sam Bennett the truth, but her mother stopped her. After promising Pilar that she wouldn't go anywhere, Theresa took advantage of Rebecca's offer to leave Harmony, and headed to the airport.
While on the plane, Theresa talked to a fellow passenger, and decided to hurt Ethan for what he'd put her through. She set up her computer with the letter and planned to send it to the tabloids. Just as she was about to send the information, the stewardess came by, and made Theresa turn off the computer. Theresa continued to wait for takeoff as there was a commotion outside...Ethan had come to tell her that he loved her! After agreeing to Gwen's idea of double-dating, Theresa and Ethan shared a romantic date at the Harmony carnival, before each going home. Earlier that evening, she had planned to tell Ethan the truth about his paternity, convinced Ethan would be hers if he weren't a Crane, but she changed her mind. When she learned Sheridan was dead she rushed to the mansion to comfort him, but was told to leave by Julian. She went home, and the next morning, was trying to send Ivy's letter to Ethan when Pilar stopped her. Theresa's dreams finally came true when Ethan proposed to her at the Church at Christmas Eve. Although Pilar begged her to erase the letter, Theresa refused. She wasn't sure if she still didn't need it. When Pilar told her that Rebecca would never forget Theresa's role in Ethan and Gwen's break-up, Theresa erased the letter from her computer. When her hard drive crashed a few weeks later, she was terrified that Ethan had found the information, but in reality, it was only a love poem she'd written about him.
On the day of their engagement party, the truth about Ethan's paternity was revealed in the tabloids. Theresa handed over all the money she saved as Gwen and Ethan's wedding planner to him, telling him it was an investment in their future. They continued to plan their wedding, and luckily, Luis and Sheridan finally got together, and they had a double wedding all planned. The day of the wedding, the tabloid published the information on which e-mail address the letter had come from...Theresa's! The wedding was in a state of chaos and Theresa ran off, spending the night at Whitney's. Ethan tried to convince Theresa that he still loved her and wanted to marry her, but she wasn't listening. She decided that the only way she could make things right was to get Julian Crane to adopt Ethan. She went down to Bermuda, where Julian was celebrating his divorce from Ivy, and the two of them ended up drunk...and married! She was horrified to realize she had married Ethan's stepfather, and vowed to keep it a secret forever. Unfortunately, she soon realized she was pregnant...and after Theresa attacked her with a firepoker to keep the marriage hidden, Ivy told Ethan everything. When Julian suggested an annulment she eagerly signed the papers, and she swore to Ethan that she never slept with Julian, promising that she would never lie to him again. She was planning to tell Ethan the baby was his, but she soon realized that she was not far enough along for that to work. So she chose a new route. She decided to have an abortion, to keep Ethan from ever finding out what she had broken her promise.
On New Year's Eve, the tabloid reporter announced that Theresa was pregnant, and that she had been seen at an abortion clinic. Theresa soon told everyone that she didn't have the abortion. Ethan automatically assumed the baby was his, and it broke Theresa's heart when she had to tell him that the baby belonged to Julian. When he realized she lied to him again, Ethan walked out on her. That same evening, Julian Crane was shot and presumed dead. Despondent, Theresa went down to the docks. As she stood on the pier, she realized that she had lost Ethan, and decided to commit suicide. She jumped into the water, and died...her soul going straight to Hell, where Julian (Zombie Charity in disguise) convinced her to sell her soul to the devil and make a pact with the darkside. After agreeing, Theresa was returned to life. Theresa soon began fulfilling her end of the bargain, although it was never revealed what her end was. She proclaimed herself Mrs. Julian Crane and moved into the mansion, trying to kick out Ivy and Rebecca, who both fought her in court for the title of Mrs. Julian Crane. Theresa won because the judge had been bought off by Alistair. When Theresa saw a video of Ethan killing Julian, she immediately confessed to the crime. She was convinced that they would never send a Crane to jail, and thought that if Ethan knew she was willing to take the blame for his crime, he would break things off with Gwen and come back to her. Her plan backfired when she was sentenced to death. Ethan helped her escape from the hospital, but when she began dreaming of their future together, he was quick to tell her that he had no plans to be with her. She had broken her word to him too many times, and he was back with Gwen.
They managed to make it to the cabin, but Theresa was in trouble...she had been hiding the fact that she was in labor because she needed time to convince Ethan that they belonged together. She was furious when Gwen showed up. Theresa watched as Gwen and Ethan shared a passionate reunion, and their connection drove her to the brink of madness. She stabbed Gwen in the back with a pair of scissors, and then went after Ethan. Both tried to stop her; they knew that she was suffering from a medical condition that was affecting her perception. They managed to get her on the couch, where she gave birth. Theresa was astonished the first time she held her son; for months she had resented the baby, blaming both the child and Julian for coming between her and Ethan, but the moment she held her son she fell in love with him, and immediately regretted that she even considered getting rid of him. Ethan and Gwen got her to the hospital, but it didn't save her. Only days after the birth of her son (whom she named Ethan Martin), Theresa was executed. And only days after she was executed, she came back from the dead. She needed to pretend to be dead so that Julian would feel safe coming back to Harmony. Although Julian wanted to get to know his son, she refused, and denied him any access because she blamed him for her break-up with Ethan. She immediately moved herself into the bedroom next to Ethan and Gwen, making plans to use the connecting door to re-establish her relationship with Ethan. Unfortunately, Ethan had moved on with Gwen. Despite Theresa's best attempts to convince Ethan that they were meant to be together, Ethan stayed with Gwen. Theresa believed she finally had the love she dreamed of when Ethan intimated that he was going to ask her to marry him, but then he asked Gwen to marry him.
Theresa wasn't ready to give up on love. She made Alistair give her a position as vice-president of Crane Industries, and used that power to make sure that no one would hire Ethan. If Ethan had to work for Crane, he was bound to realize that their love was too strong to be denied. Theresa also knew that Gwen didn't want Ethan working for Crane Industries. She arranged to have the papers validiating his employment delivered to the Church on their wedding day, and watched in anticipation as Gwen slapped Ethan across the face and walked out on him. When Gwen accused her of having something to do with it, she denied any involvement. Her heart breaks as she watches Gwen and Ethan get married. Before Theresa can focus too much on the pain of losing Ethan again, Fox Crane shows up in her bed! The two soon become fast friends. When Ivy tries to say Theresa pushed her down the stairs at the Bennett house, Theresa vows revenge on the Cranes for everything they have done to her, and launches a plan to destroy the Cranes by giving away all their money. Just as she is doing that, Julian drops a bombshell on her...they're not legally married! Theresa swore he was lying; she had eventually remembered all the details of that night, and she knew they were married. But it turns out that it was all a joke perpetrated by Julian's friend Bruce. Theresa was shocked when she realized that he was right; Julian had never actually consented to marry her, and it was only she who had said 'I do'. Julian immediately kicked Theresa out of the mansion, and turned the tables on her when he produced a writ of custody for little Ethan. Theresa was able to take the baby to Sheridan's cottage, since it, like the house, was owned by Alistair, and the writ stated only that Little Ethan could not leave the estate.
Theresa was terrified when Julian made it clear that he was going to fight for custody of his son, but she still refused to bend...Julian was not allowed anywhere near little Ethan. Julian finally caved and allowed Theresa to leave the grounds with her son, and she moved back in with her mother. Theresa was both thrilled and upset to learn that Gwen was having problems with her pregnancy. Theresa felt in her soul that the moment that baby was born Ethan would realize he made a huge mistake by marrying Gwen and leave Gwen and the baby to be with her, and Theresa felt that if the baby did die, Ethan would leave Gwen right away, but at the same time, she knew how horrible it would be to wish a baby dead so you could be with it's father. She left Harmony for Los Angeles, promising her mother that she would do nothing to interfere with Gwen and Ethan's relationship, because Theresa knew that any stress on Gwen could cause the baby to die prematurely, and she did not want to be responsible for the death of Ethan's first child. Unfortunately, when Theresa learned that Ethan and Gwen had left Harmony to see a specialist in Los Angeles (and to get away from Theresa, whom they did not realize had left town), Theresa decided that fate wanted her to be with Ethan, and formed a pact with Fox to scheme and manipulate to break up not only Ethan and Gwen, but also to break up the relationship of the girl Fox loves (Theresa does not realize it is her best friend Whitney she is scheming against).
Although Theresa and Ethan shared a few kisses, Ethan made it clear that he was committed to his wife. Theresa refused to listen, convinced that the only reason Ethan was pretending that he was going to stay with Gwen was because of the stress that Gwen was under with her pregnancy. When Gwen showed up at the complex to see Ethan, Theresa was sitting at the pool and the two ran into each other. They had an argument at the apartment complex, and Theresa made it clear to Gwen that she was going to be with Ethan, and that Ethan would be leaving her and the baby. Theresa pushed Gwen away when Gwen launched herself at her, and Gwen fell, striking her head. She was rushed to the hospital, where despite the requests of Ethan and the hospital staff, Theresa refused to leave. Even Pilar, via the phone from Harmony, told Theresa that her obsession with Ethan had caused all this pain and reminded Theresa of her promise, but Theresa refused.
When the doctor told Ethan he could only save Gwen or the baby, Theresa encouraged Ethan to let Gwen die, telling him that he had to save the baby, because that's what she would do, that's what the Church says to do. Ethan told her she was a heartless, selfish monster. Theresa then went into the hospital room, and promised Gwen that she would raise her baby with Ethan after Gwen's death. She was hustled out by security. Even after Ethan's daughter died, Theresa insisted on being there, even going into Gwen's room to be with Ethan, despite everyone asking her to leave. When it sunk in that Ethan's daughter was really dead, Theresa began to have new hope...she saw the baby's death as fate's way of bringing her and Ethan back together. Ethan has told her over and over again he wants nothing to do with her, but Theresa maintains hope that he will realize that without a child, there is no reason for him to tie himself to Gwen and he will come back to her.
Upon returning home to Harmony, Theresa was left to face the wrath not only of the Hotchkiss and Crane families, but her own mother. Pilar was disgusted by what happened in L.A., particularly because Theresa had promised her that she would not do anything to endanger Gwen and Ethan's marriage or their child. She received the ultimate shock when Julian and Rebecca announced that they would be exercising Julian's custodial rights and taking Ethan Martin from her. Despite being asked not to by Ethan, Theresa crashed Sarah's funeral, demanding that Ethan help her in her battle against Julian. She was shocked when he refused. This event led to Theresa to claim she hated Ethan, and when Chad observed that he thought Fox loved her, Theresa decided that she would marry Fox, and mused to Whitney that with Fox, she would know her financial future was secure.
Despite being ordered by a judge to stay away from her son after she attempted to kidnap him from the Crane mansion, Theresa couldn't be without her little boy, and continued to violate the court order by seeing him at the mansion. On one of these trips she ran into Rebecca. The two got into an argument, where Theresa told Rebecca that her hold on the Crane fortune was tenuous because of Julian's obvious lack of love for her, but with Fox and her son, she (Theresa) would always be a part of the Crane family. When Rebecca told her that her son would one day be a Crane servant to her own grandchildren, Theresa lashed back by stating that she hoped that Gwen and Ethan would never be able to have any children. When she realized that Gwen and Ethan knew about her heartless words, she was desperate to apologize to Gwen, realising how horrible her words were. Gwen begged Theresa to leave her alone, but Theresa insisted on apologizing. It all went wrong when Theresa told Gwen that God had punished her for marrying Ethan by killing her daughter, and that Gwen had deserved for her baby to die. Tired of asking Theresa to leave her alone, Gwen tried to remove Theresa from the room bodily. When Theresa, not ready to leave, fought with Gwen, she ended up going out the window!
In a court of law, Theresa was shocked when the judge ruled in her favor in regards to the custody of Little Ethan. Unfortunately, when she attacked Gwen and Rebecca outside the courtroom, the judge saw what she did, and he changed his decision, agreeing with children's services recommendation that her parental rights be severed. Theresa was further devastated when a different judge agreed to Ethan and Gwen's petition to adopt Little Ethan, and change his name to Ethan Winthrop Jr. Theresa finally decided that the only way to get Little Ethan back was to arrange to have herself implanted with Ethan and Gwen's fertilized egg. Even though she had not had any of the hormone treatments, Theresa kidnapped Heather (the planned surrogate) and locked her in a closet while she impersonated her at the hospital and was implanted with the eggs. She lost the embryo only a few days later, and when Fox would not sleep with her (she was planning to pass his child with her off as Ethan and Gwen's baby), she stole an experimental date rape drug from Eve Russell and after slipping it to Ethan, slipped on Gwen's nightie, spritzed her with her perfume, and donned a blonde wig, then proceeded to rape Ethan with her mother's help.
Luckily for Theresa her plan worked, and she became pregnant. While continuing to pretend that the child belonged to Ethan and Gwen, she began her attempts at blackmailing them, threatening them that if they did not give her Little Ethan, she would take their child and never let them see it. As time went on, she began to change her mind, deciding that not only would she force Ethan and Gwen to give her Little Ethan, but she would also keep the child that she had told them all along was their child. However, she continued to tell Gwen and Ethan she would give them the baby. When she learned she was carrying twins, her mother reminded her that one or both of those babies could be biologically Gwen's, yet Theresa stated that she would keep those babies regardless of who the biological mother was stated to be. When the doctors told her that she could not possibly carry both to term, she planned to have DNA tests done on the babies and abort the child that was not biologically hers, but Ethan convinced her to let the doctors make the choice and to let whichever baby was healthier live. She did, but was convinced that the surviving baby belonged to her and Ethan. She continued promising to give the child to Ethan and Gwen, who were eagerly awaiting having that baby in their home.
After the baby was born, though, Theresa made it clear she had no intentions on giving that child to Gwen and Ethan. When she announced that the child could be biologically hers, Gwen was horrified to realize that Theresa had drugged and slept with her husband (only Theresa, Pilar and Whitney know that it was rape), and that the baby might really belong to her. They waited for the DNA tests, and Gwen was destroyed when the tests proved that the child was Theresa's. Theresa was thrilled, and saw this as proof that she and Ethan were meant to be together. Unfortunately, Gwen had finally had enough and snapped, stabbing Theresa in the back with a scalpel. Theresa lost feeling in her legs and was determined to press charges against Gwen (unlike Gwen and Ethan, who had refused to press charges when a mentally imbalanced Theresa had attacked them a few years earlier). With Gwen behind bars, Theresa was convinced that she was that much closer to breaking up their marriage and getting Ethan. Not willing to let fate do the work for her, though, Theresa manipulated the situation, going so far as to fake falling down in the shower so that Ethan would have to come in to help her, and see her naked.
When Jane needed to be taken to the hospital, Theresa and Ethan were devastated when the baby disappeared, taken by Gwen. While waiting for word on their child, Theresa did everything she could to get Ethan to come to her again. Ethan continued to resist her advances, and when she and Ethena found Gwen with the baby at the Crane compound, Ethan made a deal with her. He would not fight for custody of the baby as he had planned if she would not press charges against Gwen. He reminded her of the many time he and Gwen had not pressed charges against her, and Theresa promised not to press charges. He warned her that if she broke her promise, he would fight for custody of Jane as he had originally planned.
When they returned to Harmony, Theresa broke her promise to Ethan and pressed charges against Gwen, convinced that if she could get Gwen sent to prison that Ethan would have no choice but to turn to her. Ethan made good on his word as well -- he followed through with his original plan to fight for custody. Gwen was found not guilty due to a medical interaction, and Theresa lost custody of Jane. Initially temporary, Gwen and Ethan soon had full rights. Theresa would not stop in her quest to get both Ethan and Jane back. When her numerous attempts to seduce Ethan didn't work, she married Alistair Crane in the hopes of getting Jane back, and inevitably Ethan. She made a deal with Alistair that she would do whatever he wanted, including sleep with him, in exchange for being Mrs. Alistair Crane. Alistair legally adopted her son, changing his name to Ethan Lopez-Fitzgerald Crane, and Theresa began a time of terror as his wife, with many of their sexual encounters being forced on Alistair's behalf.
Theresa also continued her plots to destroy Ethan and Gwen's marriage. When Ethan wouldn't bow to her wishes, she made certain that he could not get a job anywhere, and arranged for Gwen to get a job that would keep her away from home, and Ethan. So determined was she to get Ethan that she flew to Rome to locate the tabloid editor who had initially printed the story about Ethan's paternity. She found J.T. Cornell in Rome and convinced him to spill the beans for ten million dollars, but Ethan refused to believe him, considering what Theresa had offered to pay him.