Thomas Forrester was the first-born child of Ridge Forrester and Taylor Hayes. While Taylor was pregnant, Ridge's brother, Thorne Forrester, and Ridge's on-again-off-again wife, Brooke Logan, worked to keep Ridge and Taylor apart. Thorne had fallen for Taylor and convinced her to tell Ridge the baby was Thorne's. Taylor went into labor en route to Ridge and Brooke's wedding, and gave birth in Thorne's car. Taylor finally told Ridge the truth, and the baby was named Thomas after St. Thomas, where Ridge had originally proposed to Taylor.
Baby Thomas was briefly the target of the infamous Sheila Carter, who wanted to keep her nemesis, Stephanie Forrester, away from her husband, James Warwick. Sheila snuck into Ridge and Taylor's house and snipped a lock of Thomas' hair, presenting it to Stephanie and threatening to kill Thomas if Stephanie didn't heed Sheila's warning.
Thomas and his family were devastated when Taylor was killed in an altercation with Sheila. After a period of mourning, Ridge remarried Brooke, who stepped in as a mother to Thomas and his two twin sisters, Steffy and Phoebe Forrester. Brooke's oldest daughter, Bridget Forrester, also played a guardian role, so Thomas was angry when he found out that Brooke once had an affair with Bridget's husband, Deacon Sharpe. Thomas drank a whole bottle of vodka and wound up in the hospital.
Soon Thomas was in high school and crushing on Caitlin Ramirez. Caitlin's father, Hector Ramirez, disapproved because he "didn't like rich people." By the time Hector warmed up to Thomas, Rick Forrester had also become interested in Caitlin. After Caitlin chose Rick, Thomas started seeing Rick's ex-wife, Amber Moore. Ridge's efforts to keep the much older Amber away from Thomas included a restraining order. Amber overheard Ridge talking about his previous feelings for Bridget. Amber tried to neutralize Ridge, first by taking an "incriminating" photo of Ridge and Bridget, then by trapping them in a mineshaft rigged with cameras in the hope they'd kiss. Thomas left Amber when he found out how Amber had targeted his father, then resumed his relationship with Caitlin.
Thomas bonded with Gabriela Moreno, who had also lost a mother. But Taylor turned up alive: Prince Omar had healed Taylor at his palace in Morocco and put a wax dummy in Taylor's coffin. Thomas was overjoyed and campaigned for Ridge to return to Taylor. Caitlin was jealous of Gaby, and later Thomas broke up with Caitlin to be with Gaby. Thomas took a designing job at Spectra Couture when Forrester Creations denied him an internship. Gaby was an illegal alien, so when attorney Connor Davis hinted Thomas could keep Gaby in the country by marrying her, Thomas and Gaby eloped to Las Vegas. Ridge wanted the marriage annulled.
Taylor agreed to help deceive a visiting immigration agent if Thomas and Gaby refrained from having sex. But when Thomas and Gaby made love, Taylor turned Gaby in. However, Thomas and Gaby's marriage was declared legal because they were both of age and had consummated their union. Ridge challenged Thomas to a teen fashion showdown: if Ridge won, Thomas would annul his marriage. If Thomas won, Thomas could accept the generous designing contract offered him by Spectra. Thomas worked hard, but lost the challenge after Ridge stacked the deck. Thomas annulled his marriage, but Taylor saw to it that Gaby could stay in the United States legally.
Thomas went away to college. In the meantime, Thomas' sister, Phoebe, had been upset because Rick dated her, her mother, and her sister. Phoebe confronted Rick in his car and died in a crash. Later, when things got serious between Rick and Steffy, Rick's house was set ablaze and his car exploded. Stephanie's wacky sister, Pam Douglas, was jailed, but Thomas admitted he'd done it because he hated Rick and wanted to scare him away from Steffy. Rick tried to blackmail Ridge to keep Thomas out of jail, although Rick later relented and let Thomas work at Forrester. Thomas underwent counseling with James to deal with his anger, and eventually made peace with Rick.
Ridge and Taylor were going to remarry, so Thomas and Steffy intercepted and faked text messages between Ridge and Brooke to make sure Taylor's wedding took place, but Brooke exposed them. Thomas became Steffy's confidant and suggested that Steffy seduce Bill Spencer, Jr. to regain control of Forrester. But after Thomas came back from Forrester International, Thomas blasted Steffy for that very move after hearing of Steffy's attempts to blackmail Brooke. Thomas was hurt when Taylor gave Steffy her full 25% share of Forrester, while Thomas got nothing. Thomas stuck up for Brooke in a meeting, and included her in an idea to revive the Forrester men's line. Taylor was violently opposed and didn't want Thomas anywhere near Brooke.
Thomas feared his collection would get lost under Forrester's very popular Hope For The Future line until Taylor's then-husband, PR whiz Whip Jones, suggested Thomas needed a gimmick. Thomas kissed Brooke on the runway, earning his line the name "Taboo." Thomas became attracted to Brooke and kissed her while she was sleeping, even as Thomas was dating Dayzee Leigh. Brooke and Thomas were in a plane crash after promoting Taboo, washed up on a deserted island, and hallucinated from eating psychedelic berries. They were rescued, but didn't know if they'd only hallucinated having sex. Stephanie promised Thomas her 25% stake in Forrester if Thomas said the sex happened. Ridge left Brooke and dashed to remarry Taylor, while Dayzee begged Thomas to confess. After the truth came out, Dayzee dumped Thomas, Taboo was cancelled, and Thomas was "banished" to work in the Forrester basement with Thorne, who wondered if Thomas might be gay.
Thomas took an interest in Brooke's daughter, Hope Logan, and whisked Hope off to Cabo San Lucas, not knowing that Steffy was there with Hope's ex-fianc�, Liam Cooper. Thomas proposed to Hope and worked with Steffy to keep Hope away from Liam, but the scheme backfired. Later, Thomas and Rick competed for the attention of Caroline Spencer. When Caroline brought Thomas home to meet her mother, Karen Spencer, Thomas asked about Caroline's father and was stunned to be introduced to Danielle, Karen's spouse and Caroline's second mother. Caroline was pleased when Thomas accepted Karen and Danielle wholeheartedly.
Thomas continued dating Caroline and encouraged Marcus Forrester when he got cold feet before his wedding to Dayzee. When Marcus was arrested for hitting Dazyee's friend Anthony with his car while texting, Thomas and Caroline investigated and discovered that Anthony had been hit beforehand, and that Marcus had only hit a pothole. Later, Rick played on Thomas' former feelings for Hope and set them working together in an attempt to win Caroline for himself. Thomas was conflicted and kissed Hope twice, once as a publicity stunt and once on his own, but ultimately Thomas chose to be with Caroline.
However, when an absentee Ridge appointed Thomas interim CEO, Thomas and Rick got into an altercation that ended with Rick crashing through a second-story window. Caroline was horrified that Thomas would resort to violence, and dumped Thomas for Rick. Thomas began letting his CEO position go to his head and threw his weight around, even telling Brooke she was no longer family but only a valued employee. Thomas wanted to layer technology into the running of Forrester and tried to implement a slew of upgrades, but Rick had Eric step in and limit the ideas to trial runs.
When Stephanie died, Thomas was ready to use his clout as Forrester's biggest stockholder to realize his vision. But Stephanie left behind a DVD in which she announced she'd found a loophole in the company's original Articles of Incorporation, allowing her to instead transfer the stock to Eric and name him CEO. Thomas was furious that he had no legal grounds to appeal. Eric challenged Thomas and Rick to a fashion duel and offered to mentor the winner as Forrester's president. Thomas swore he would bury "the Logans", but when Eric deemed Rick the winner, Thomas decided to move to Paris, which upset Taylor. Eric responded by promoting Thomas to vice president and telling Rick he had to respect Thomas' ideas.
Sales started slipping at Forrester under Rick's leadership, so Taylor encouraged Eric to hear Thomas' progressive ideas again. But during Thomas' presentation, Brooke interrupted with a mini showing of the once successful Brooke's Bedroom lingerie line. Eric green-lit the reboot and again shelved Thomas' marketing concepts. Thomas almost came to blows with Rick when Thomas declared that no one was going to want to see a 50-year-old woman modeling lingerie. Thomas found some comfort in attending sister Steffy's unusual wedding, which included Steffy riding up the aisle on a motorcycle wearing a black dress/suit ensemble Eric had designed.