Ridge and Taylor Forrester were expecting, but Taylor had a difficult pregnancy due to tuberculosis. However, Taylor safely delivered healthy identical twins, Steffy and Phoebe. Steffy was named for her grandmother, Stephanie Forrester. During a family boat trip in St. Thomas, two-year-old Steffy fell overboard and was presumed dead in a shark attack. But Morgan DeWitt, a deranged woman who had once been forced by Stephanie to abort Ridge's baby, had actually kidnapped Steffy. Morgan dyed Steffy's hair red to match her own so she could raise her. Ridge and Taylor rescued Steffy, and Morgan was institutionalized.
In 2002, Taylor was killed in an altercation with Sheila Carter. After a period of mourning, Ridge remarried Brooke Logan, who helped raise Steffy and her siblings. They didn't know that Taylor's former husband, Prince Omar of Morocco, replaced Taylor's body with a wax dummy and healed the real Taylor at his palace. When Taylor reappeared in 2005, Ridge returned to her, reuniting Steffy with her family. However, the following year, Taylor revealed that long ago she had slept with James Warwick, which torpedoed her marriage to Ridge. Steffy and Phoebe left to attend boarding school in London, although Phoebe returned by herself in 2006.
Steffy, now fraternal twins with Phoebe instead of identical, arrived home in 2008, determined to work her way up at Forrester Creations. She started in the shipping department, where she met Marcus Walton. When Donna Logan took over at Forrester, Steffy dug up dirt and found out that Donna was Marcus' birth mother. Though Ridge disapproved of Steffy dating Donna's son, things went well until Rick Forrester got control of the company himself and sent Marcus to Forrester International so Steffy would be available. But Rick had also been involved with Phoebe and Taylor, leading an angry Phoebe to confront Rick in his car. Phoebe got physical, causing a crash in which she died. Steffy initially blamed Rick, but bonded with him as she grieved, leading to a kiss.
Marcus returned and wanted to marry Steffy, but by then Steffy was more interested in Rick. When the secret relationship was exposed, Ridge fumed because of Rick's part in Phoebe's death, and Steffy found the entire family against her, including her brother Thomas, who almost killed Rick in an explosion that was meant to scare him. Steffy agreed to marry Rick. But Rick resented Ridge's treatment of Brooke over the years, and had only proposed to Steffy to hurt Ridge and ruin his marriage to Brooke. Rick boasted about it to Ridge, but Ridge recorded the conversation. Steffy dumped Rick after hearing it, then briefly took him back before finally realizing that their relationship would never withstand all the family opposition. Marcus later tried unsuccessfully to revive things with Steffy.
Steffy was thrilled when Ridge ended up going back to Taylor on his own. But as their wedding approached, Steffy faked text messages to Brooke to make sure the marriage happened. Brooke found out and stopped the wedding, cementing her place as Steffy's enemy. Steffy was attracted to Owen Knight, who was married to Jackie Marone. Owen was tempted by Steffy's overtures, but remained faithful to Jackie.
Bill Spencer, Jr., acquired Forrester Creations, and Steffy became intrigued by the older man. Steffy's ingenuity earned her a promotion to Head of Public Relations. Bill was engaged to Katie Logan, though he didn't mind when Steffy kissed him. However, Steffy minded when Bill married Katie and made her CEO of Forrester. Katie offered her sisters the leadership positions the Forrester men turned down, which set Steffy on an anti-Logan campaign. Steffy used the attraction between her and Bill to get the company back into Forrester hands. She arranged a seduction and swiped Katie's engagement ring from Bill's bedroom before any lovemaking could take place. Steffy threatened to tell Katie how she got the ring if Bill didn't sign the company over to her. Steffy edged the Logans out by dividing the company's stock equally between Ridge, Stephanie, Eric, and Taylor.
Stepping up her battle against the Logans, Steffy tried to seduce Oliver Jones, the boyfriend of her step-sister, Hope Logan. Oliver didn't bite, but Steffy did manage to publicly embarrass Hope at a showing for her Hope For The Future fashion line by rigging the sign to read "Ho" For The Future. When Oliver inadvertently videotaped Brooke's daughter, Bridget Forrester, cheating on her husband, Steffy wanted to use the footage to hurt Brooke's family, but Oliver talked her out of it. Instead, Steffy went for the jugular after Brooke "accidentally" had sex with Oliver at Hope's graduation party, where everyone wore masks. Steffy told Brooke she wouldn't go public about the tryst if Brooke left Forrester and sent Hope away to college. Oliver also had to date Steffy. Brooke defused Steffy's bomb by telling Ridge about Oliver herself. A forgiving Ridge forced Steffy to craft a video tribute to Brooke.
Computer tech Liam Cooper mistakenly recorded Steffy talking to Ridge about Brooke's betrayal. Justin Barber, Liam's boss at Spencer Publications, coerced Liam into augmenting Steffy's video with the recording, betting that Brooke's scandal would help sell magazines. Ridge fired Steffy when the video went public, but Steffy got Liam to help clear her name. Taylor demonstrated her faith by gifting Steffy with her 25% share in Forrester. Angry with Ridge, Steffy momentarily considered selling the stock to Bill, who still wanted the company. Steffy instead transferred to Forrester International after making a few moves on Liam, who had started dating Hope.
Steffy came home with Bill Spencer on her mind. She recalled their flirtations and declared that she was a better match for Bill than Katie. Steffy claimed to understand Bill's motivation after saving Amber Moore from Bill's murder plot, which prompted Katie to walk out. Later, Steffy desperately asked Bill for help when Thomas went missing at sea. Bill declared his love for Steffy after the rescue brought them closer, but he refused to leave Katie. Steffy was overjoyed when Ridge divorced Brooke and planned to remarry Taylor upon learning that Thomas and Brooke had sex on a deserted island while hopped up on psychedelic berries. But Ridge returned to Brooke when it turned out Thomas lied about the encounter because Stephanie promised him her stock. Feeling abandoned, Steffy sought comfort in Bill's arms. Bill promised to leave Katie, but Katie had a heart attack when Taylor exposed the affair. Devastated when Bill opted to stay with Katie, Steffy slipped in her bathtub, hit her head, and almost drowned. But Bill's son, Liam, had stopped by to return Bill's key and saved Steffy, who developed a crush on Liam.
Liam's fianc�(c)e, Hope, wanted to remain a virgin until her wedding night. Steffy gave Liam a shoulder to cry on and let him know she was sexually available. Hope saw Liam kissing Steffy and broke things off in a cell phone message. Confused, Liam found Hope's engagement ring on his mantel and offered it to Steffy instead. But Steffy knew that Liam and Hope would reunite if they got a chance to talk. So Steffy went to Bill, who arranged a trip to Aspen, Colorado for Steffy and Liam. Hope found out and followed, but, thanks to Steffy and Bill, Hope got trapped in a gondola above a ski slope and was forced to watch Steffy and Liam exchange vows.
Steffy sensed that Liam still thought of Hope, so Bill sent Liam away with Steffy to Cabo San Lucas. Coincidentally, Hope, who had been spending time with Thomas, ended up at the same resort. Steffy and Thomas worked to keep Liam and Hope from seeing each other, but the attempt backfired, leading to an ATV chase in which Steffy was seriously injured. At the hospital, Liam wanted an annulment when Steffy confessed her deceptions in Aspen and Cabo. Bill faked Steffy's MRI so it said she had a blood clot that could become fatal under stress. Liam felt obligated to stay with Steffy, but Katie got suspicious and eventually uncovered Bill's machinations. Steffy was horrified that Bill would make her parents think she was going to die.
Steffy held out for a proper divorce from Liam, feeling an annulment would deem their marriage invalid. Rick used his past with Steffy to get the annulment papers signed for Hope. But Steffy had written "loser" in place of a signature, halting Liam and Hope's wedding. Steffy was sure Liam would be back if she waited it out. Steffy created a ski line and attended Aspen's Fashion Week, which also brought Liam out to cover the event. Hope made the trip as well, but she was abusing antianxiety medication, so strung out when she went skiing that she crashed into Steffy. Liam was furious, and stayed by Steffy's side in the hospital, where Steffy had a change of heart and signed the annulment papers. When Liam tore them up, Steffy felt she still had a chance, but ultimately, Steffy told Liam to marry Hope.
Having forged a tentative friendship with Hope, Steffy hesitated accepting an invitation to Hope's wedding in Puglia, Italy. Bill hinted the tide could turn in Steffy's favor, so Steffy attended. Steffy was at Liam's side when he found a note that implied Hope had jilted him, so Liam kissed Steffy and prepared to away with her on the Spencer jet. But Hope returned and explained that the appearance of her estranged father, Deacon Sharpe, had delayed her. Steffy overheard the conversation and again encouraged Liam to marry Hope. Steffy watched the ceremony from afar but slipped and fell into the Adriatic Sea. Steffy was furious when she discovered that Bill had sprung Deacon from jail in an attempt to push Liam back toward Steffy.
An iPad had accidentally recorded video of Liam and Steffy making out in Italy. Steffy deleted it but first e-mailed a copy to herself. Ultimately, Hope saw it and declared she hated Steffy before insisting on a fresh wedding to Liam. The night before the ceremony, Steffy "kidnapped" Liam to a club to show him how much fun his life could be without Hope. When a hung over Liam arrived for his wedding sporting dyed hair and a tattoo, Hope washed her hands of Liam, and Steffy let Liam know they could have a wonderful relationship when he was ready.
Liam sought Steffy out after a failed attempt to reunite with Hope, so Steffy took him to a "secret cabin" on Brooke's property where she had spent time with Ridge as a child. Steffy and Liam made love there, which Donna Logan saw and reported back to Bill and Brooke. Steffy was happy to finally have reunited with Liam.
Steffy and Liam's flight to Hawaii was diverted to Aspen when Bill and Brooke needed the Spencer jet to look for Katie, who had disappeared during a bout with postpartum depression. Steffy helped Liam look after his new baby brother, Will. When it was evident Katie wasn't in Aspen, Steffy and Liam found time to go parasailing together. Returning to Los Angeles, Liam asked Steffy to move in with him. Steffy agreed, but kept her penthouse loft in an effort to maintain her independence.
Ridge, who had relocated to Paris, wanted Steffy to visit. Steffy and Liam made love; later, Steffy found out she was pregnant. Steffy rushed to tell Liam but spied Liam kissing Hope in their bedroom. When Taylor found Steffy's pregnancy test, Steffy ordered her mother to keep it a secret. Instead, Steffy told Liam he could use the time to explore his residual feelings for Hope as long as he didn't cross the line. Steffy was comforted when Liam said he'd remain loyal. But when Steffy called Liam at home and found out Hope was with him, Steffy was upset. Steffy flew home to tell Liam about their baby but kept mum after Liam, who wanted time to decide between Steffy and Hope, asked Steffy to move out.
While arguing with Hope over Liam, Steffy bashed Brooke, prompting Hope to shove Steffy into a desk. Steffy hit the desk belly-first, but later, when Taylor accompanied Steffy to her sonogram, Steffy's unborn child did not appear to be harmed. Steffy found out that Brooke had planned a surprise wedding for Hope and Liam, which Steffy stopped with the announcement of her pregnancy. When Liam chose to make a home with Steffy and the baby, Steffy offered to let Liam go if he wasn't absolutely sure, unaware that Hope had encouraged Liam to marry Steffy before the baby was born. Steffy was thrilled when Taylor announced that Eric had agreed to have the wedding in the Forrester courtyard.
Unlike Steffy's Aspen wedding to Liam, Steffy's family was in attendance (except for Ridge), and Steffy shocked them all by riding up the aisle on a motorcycle, wearing a black dress/suit ensemble that she had gotten Eric to design. Liam surprised Steffy by having her "all-time favorite" singer, Julia Michaels, perform at the reception. Steffy then correctly guessed that Liam had arranged for their honeymoon to be in Aspen, and she and Liam even considered naming their child Aspen in honor of their favorite place.
Liam and Steffy gleefully bought baby clothes and picked out colors for the nursery. Steffy then paid a visit to Thomas, who had moved into Taylor's old beach house with Oliver. Steffy told Thomas how happy she and Liam were, unaware that a tearful Hope was within earshot. Steffy empathized with Hope and was so moved when Hope broke down and admitted she was happy for Steffy that Steffy hugged her rival. Not wanting to keep Liam waiting, Steffy decided to dodge a traffic jam by riding her motorcycle home, though she had promised Liam she wouldn't ride while pregnant. A car darted in front of Steffy, causing her to wipe out, and she was immediately taken to the hospital.
Having suffered another concussion, on top of the concussions she'd had before, Steffy's memory was fuzzy, and Steffy didn't remember being pregnant. But, with Liam's coaching, Steffy put the pieces together and was horrified to learn she had lost their baby. Steffy went into a deep depression, with Taylor pleading with her not to blame herself for riding the motorcycle. Steffy took a baseball bat to the bike and latched on immediately when Taylor suggested that Steffy and Liam have another baby.