Tried to set Rick Forrester's house on fire 
Blew up Rick Forrester's car 
Punched Rick Forrester so his family could perform an intervention on his sister, Steffy 
Faked text messages to keep his father from reuniting with Brooke Logan 
Lied that he'd had sex with Brooke Logan in exchange for Stephanie Forrester's stock 
Deceived Hope Logan in Cabo San Lucas to keep her from seeing Liam Cooper 
Shoved Rick Forrester, causing him to crash through a second-story window 
Had sex with Caroline Forrester when she was too incapacitated to specifically consent 
Punched his father, Ridge Forrester 
Thomas Forrester is the first-born child of Ridge Forrester and Taylor Hayes. While Taylor was pregnant, Ridge's brother, Thorne Forrester, wanted to claim Taylor's baby as his since Thorne was in love with Taylor, who was on the outs with Ridge. Soon Taylor and Ridge reunited and named their baby 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 snipped a lock of Thomas' hair and presented it to Stephanie, 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. Thomas and his twin sisters, Steffy and Phoebe Forrester, eventually gained a stepmother in Ridge's longtime love, Brooke Logan. Thomas, who had also come to depend on Brooke's daughter, Bridget Forrester, was angry when he found out Brooke once had an affair with Bridget's husband, Deacon Sharpe; Thomas downed a whole bottle of vodka and had to be hospitalized.
In high school, Thomas crushed on Caitlin Ramirez, whose father, Hector Ramirez, didn't like rich people. Thomas was relieved when Hector warmed up to him, but soon Thomas had to battle Brooke's son, Rick Forrester, for Caitlin's affections. After Caitlin chose Rick, Thomas started seeing Amber Moore, Rick's ex-wife. Thomas couldn't believe it when Ridge got a restraining order to keep Amber away from him, but Thomas was even more shocked when Amber tried to ruin Ridge's life by getting him to act on his inappropriate feelings for Bridget. Thomas left Amber and reunited with Caitlin.
Thomas bonded with Gabriela Moreno, who had also lost a mother. But after Taylor turned up alive, Thomas campaigned for his parents to remarry. Thomas assured Caitlin she had no reason to be jealous of Gaby, but soon Thomas left Caitlin for Gaby and took a designing job at Spectra Couture, the rival of family design house Forrester Creations, because Forrester denied Thomas an internship. Since Gaby was in the U.S. illegally, Thomas took the advice of attorney Connor Davis and married Gaby in Las Vegas. Thomas accepted Ridge's challenge to a teen fashion showdown; if Ridge won, Thomas had to annul his marriage. Thomas lost the challenge and got the annulment, but made sure Gaby could stay in the country legally.
Thomas went away to college but was furious to learn that Rick had romanced his mother and both his sisters while Thomas was gone. After Phoebe died confronting Rick, Thomas tried to scare Rick into leaving Steffy by setting Rick's house ablaze and blowing up Rick's car. Thomas underwent counseling with James and eventually made peace with Rick, who had broken things off with Steffy. Thomas and Steffy later faked text messages between Ridge and Brooke to make sure Ridge's remarriage to Taylor took place, though Brooke exposed the siblings at the ceremony.
Publishing magnate Bill Spencer, Jr. gained control of Forrester Creations, so Thomas suggested that Steffy seduce Bill to get the company back, later blasting Steffy for doing exactly that when Steffy also tried to blackmail Brooke. Thomas stuck up for Brooke in a meeting and included her in an idea to revive her men's line. To call attention to the collection, which Thomas renamed Taboo, Thomas kissed his sometime stepmother on the runway when PR whiz Whip Jones suggested Thomas pull a publicity stunt, which enraged Taylor. Thomas became fascinated with Brooke and kissed her as she slept, even though he was dating Dayzee Leigh.
En route from a Taboo promo tour, Thomas and Brooke nearly died in a plane crash and were stranded on a deserted island. Forced to eat hallucinogenic berries to survive, Thomas wasn't sure if he'd actually slept with Brooke or just imagined it. Once home safe, Thomas accepted a bribe from his grandmother, Stephanie Forrester: if Thomas would help keep Ridge and Brooke apart by lying that Brooke had sex with Thomas on the island, Thomas would earn Stephanie's 25% share in Forrester. Thomas nearly went through with the plan but came clean after Dayzee begged him to; Thomas lost both Dayzee and Taboo and found himself "banished" to 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, where Steffy happened to be vacationing with Hope's ex-fiancé, Liam Cooper. Thomas worked with Steffy to keep Hope away from Liam, but the scheme backfired. Later, Thomas competed with Rick for the attentions of Caroline Spencer, who had two mothers, Karen Spencer and Danielle. Thomas wholeheartedly accepted Karen and Danielle's relationship, and later helped Caroline clear their buddy Marcus Forrester, who thought he had hit Dayzee's friend Anthony with his car while texting. Thomas remained conflicted about Hope and kissed her twice, but ultimately chose to stay with Caroline.
After Thomas became interim CEO of Forrester in Ridge's absence, Thomas butted heads with Rick, who wanted Caroline for himself; Thomas lost Caroline when Rick crashed through a second-story window because of their argument. After Stephanie died of lung cancer, Thomas was ready to use the 25% share Stephanie promised him to implement his new ideas, but Stephanie left behind a DVD that ultimately transferred all CEO power to her widower, Eric Forrester. Thomas had to battle Rick in a fashion showdown for the presidency of Forrester, which Rick won.
Thomas hit the runway with other male Forrester executives for Caroline's cancer foundation fundraiser. Later, Thomas moved into his childhood beach house and roomed with his friend, Oliver Jones. Thomas became a sounding board for Steffy and Taylor, then failed to convince Eric that Thorne would make a better president than Rick. Thomas eventually moved to Paris to work with Thorne at Forrester International and watched as his cousin, Aly Forrester, had an unusually intense negative reaction to Hope's boyfriend, Wyatt Fuller.
Thomas agreed to sign his 5% stake in Forrester over to Ridge, who wanted to combine his stock with Steffy's and Bill's to overthrow tyrannical CEO Rick. After Aly, who had a history of mental illness stemming from the tragic childhood loss of her mother, died in a confrontation with Steffy, Thomas came home for Aly's memorial. Thomas still had feelings for Caroline, who had moved on with Ridge; when Ridge suddenly dumped Caroline because he couldn't give her the family she wanted, Thomas' comforting turned to lovemaking after too much wine. Thomas was taken aback when Caroline didn't remember sleeping with him because she had also taken antianxiety pills; Thomas swore he wouldn't have initiated sex if he'd realized she'd been so incapacitated. Thomas and Caroline agreed to forget the evening ever happened.
Thomas became a womanizer, kissing Forrester intern Nicole Avant and bedding a bevy of other girls; after Ridge blasted Thomas for crossing the line with co-workers, Thomas punched Ridge, which got him shipped back to Forrester International. When Thomas came back, he found out Caroline was pregnant; satisfied to hear the child was Ridge's, Thomas moved in on Wyatt's girlfriend, Ivy Forrester, and bet Steffy he could get Ivy into bed. Thomas and Wyatt blamed each other when Ivy was electrocuted during an argument with Steffy, who had told Wyatt about Thomas and Ivy's kisses.
Thomas experienced an epiphany and gave up playing around when Caroline gave birth to baby Douglas, whom Ridge had named in honor of Stephanie's maiden name; Thomas felt a strong connection to his little brother. But when Ridge announced that Thomas was really Douglas' father, and that Caroline had known all along, Thomas took off with Douglas and summoned Caroline to the Forrester cabin in Big Bear. Thomas agreed to let Ridge raise Douglas to avoid a scandal, but once Bill nearly went public with Douglas' paternity, Thomas changed his mind. After Caroline, who had split from Ridge, declined Thomas' offer to be a family with Douglas, Thomas befriended Nicole's half-sister Sasha Thompson and defended her from her bullying father, Julius Avant. Thomas built on Sasha's thank-you kiss by dating her though he still felt pulled toward Caroline.