Steffy, named after her grandmother Stephanie, was born just a few minutes before her fraternal twin sister, Phoebe. Taylor suffered from tuberculosis during her pregnancy but survived the complicated delivery.

Ridge and Taylor took the twins and their older brother, Thomas, to Saint Thomas, where the couple renewed their wedding vows. During a boat trip, two-year-old Steffy fell overboard during stormy weather and was presumed dead. However, Steffy had been kidnapped by Morgan DeWitt, a deranged ex of Ridge's. Taylor grew suspicious of Morgan and was shocked to discover Steffy in Morgan's house. Morgan held mother and daughter captive, but Ridge eventually saved his wife and child by driving his car through Morgan's house as she was about to shoot Taylor. Morgan was committed to a psychiatric institution. Following the presumed death of their mother, Steffy and Phoebe were sent to boarding school in London, England. Steffy returned to L.A. at her father's request and started working in the shipping and receiving department of Forrester Creations, determined to work her way up in the business. She befriended Marcus, and Pam enlisted Steffy to check into Marcus' background. Steffy discovered that a teenage Donna had given up Marcus for adoption. Steffy promised Marcus to keep his maternity a secret, but Phoebe overheard their conversation and revealed the secret to Ridge. Phoebe and Ridge insisted that Steffy stay away from Marcus, but Steffy ignored their requests.

Steffy and Marcus admitted their attraction and shared their first kiss when he comforted her after Eric suffered a heart attack. Steffy and Marcus fell in love, despite Ridge's disapproval. Steffy was livid when Eric named Rick president of Forrester Creations, and she was further disappointed when Rick sent Marcus to work in the company's international office.

Steffy slapped Rick when he tried to kiss her during a business dinner, and she soon realized he had intentionally reassigned Marcus so Rick could pursue her to irritate Ridge. She was later devastated when Phoebe died in a car accident, and at first she blamed Rick, who had been driving. She softened after Bridget provided DNA evidence that Phoebe had physically attacked Rick while he had been driving. Steffy and Rick bonded over Phoebe's death, and though they tried to deny their feelings due to their families' disapproval, they shared a handful of passionate kisses. Marcus returned from Paris and wanted to whisk Steffy away to a weekend at Big Bear. She was shocked when Marcus proposed at the cabin, but she explained that things had changed since Phoebe's death, and she ended their romantic relationship. After Marcus left, Rick showed up and declared his love, and they made love for the first time.

Rick and Steffy agreed to keep seeing one another in secret. Back at work, Rick offered Steffy a ride to pick up some fabric, and Ridge had a flashback to Phoebe's accident. Ridge demanded that Rick never go near Steffy again. Steffy tried to break things off with Rick, but they couldn't stay away from one another.

Stephanie inadvertently found out about Rick and Steffy's affair, and as their secret spread, other family members voiced their disapproval. Rick impulsively proposed to Steffy, but she turned him down. Rick earnestly asked Ridge for Steffy's hand in marriage, but Ridge refused. After there appeared to be multiple attempts on Rick's life, Taylor, Ridge, and Thomas forcibly took Steffy to Big Bear, where Thomas confessed that he'd tried to scare, but not kill, Rick.

Steffy struggled with whether or not to tell Rick the truth, but Rick figured it out for himself and used it as leverage against Ridge. Rick and Steffy got engaged, but Ridge secretly recorded Rick admitting that he planned to marry Steffy to seek revenge on Ridge. After Steffy heard the tape, she angrily broke up with Rick. Steffy forgave Rick after he gifted her with a tribute DVD he'd created in Phoebe's memory, and she agreed to give him another chance, even though her family pushed her to reunite with Marcus. Eventually, Rick and Steffy's romance fizzled when they realized their families would never be at peace as long as they were together. Marcus tried to revive his romance with Steffy, to no avail.

Steffy was thrilled when Ridge and Brooke became estranged, and he and Taylor decided to remarry. Steffy intercepted text messages from Brooke to Ridge, and she tried to lead Brooke to believe that Ridge wanted nothing to do with Brooke. When Brooke refused to give up, Steffy sent a message requesting that Brooke meet Ridge at their special place on the beach at the time he was scheduled to marry Taylor. Brooke revealed Steffy's scheme when she interrupted the wedding. Steffy continued to push for her parents to be together.

Steffy and Owen became friends, and she respected his love for Jackie, but questioned whether or not he was satisfied with his marriage. Jackie warned Steffy to stay away from Owen. Steffy surprised Owen with an impulsive boat trip on the Shady Marlin, and during the course of their journey, she lost her footing and fell overboard. Owen rescued her and performed CPR to save her life. At one point, Owen and Steffy almost kissed, but he stayed true to Jackie.

Steffy was resentful when the Logan sisters took charge of Forrester Creations after Bill acquired the company and named Katie CEO. Steffy accepted the role as head of PR at Forrester after she impressed Katie and Bill with her ideas for a new line. Steffy developed a fascination with Bill, and she planted a kiss on him while thanking him for believing in her. The day before Bill's wedding to Katie, Steffy summoned him to Big Bear to discuss the kiss, but he assured her it was no big deal and agreed to keep it a secret. Steffy kissed him again.

Katie fired Steffy after Bill told her about the kisses, but she reluctantly reinstated Steffy to keep peace between the Forresters and the Spencers. Steffy vowed to find a way to return control of the company to the Forresters. She conspired with her family to design a horrendous line that would force Bill to sell off the company. Steffy's hatred toward the Logans intensified when Brooke ruined their scheme by confessing it to Katie. Steffy tried to get Bill to leave Katie, and their heated conversation escalated into yet another kiss.

Steffy became incensed when Brooke hired Hope to work at Forrester, especially when Katie selected Hope's "Hope for the Future" line over one of Steffy's ideas. Steffy attempted to seduce Bill into returning the company to the Forresters, but just as they were about to have sex, they heard Katie arrive home. Steffy swiped Katie's engagement ring before she scurried out. When Bill opted to stay with Katie, Steffy blackmailed Bill into selling her back Forrester Creations. The deal Steffy crafted made Ridge, Eric, Stephanie, and Taylor equal partners, and intentionally excluded the Logans.

Steffy learned that Oliver had accidentally videotaped Owen and Bridget having sex, and she flirted with Oliver to gain access to his phone to steal a copy of the video. Steffy intended to use it to force Brooke to leave Forrester Creations. When she explained her motivations to Oliver, he saw her vulnerable side, and they kissed. Steffy pursued Oliver, even though he made it clear he was interested in Hope. Steffy and Pam conspired to humiliate Hope during Hope's first press conference, and Steffy was crushed when Ridge removed her from the "Hope for the Future" campaign. Steffy tried to seduce a sexually frustrated Oliver, but he resisted temptation.

Steffy stumbled upon the revelation that Brooke and Oliver had sex at Hope's graduation party. Steffy tried to blackmail Brooke into leaving Forrester, and she also demanded that Oliver date Steffy and talk Hope into attending college on the East Coast. At first, Brooke and Oliver agreed, but when Steffy insisted that Brooke also convince Donna not to sue for half of Eric's shares in their divorce settlement, Brooke decided to confess all to Ridge, who forgave her.

Ridge demanded that Steffy abandon her blackmail attempts, and he punished her by assigning her to assemble a tribute to Brooke. Steffy put her best effort into the tribute, but unbeknownst to her, Liam had accidentally recorded her conversation with Ridge while Liam had been fixing her computer. Justin stumbled upon the recording and altered the tribute to expose Brooke and Oliver's tryst. Ridge assumed Steffy was responsible, and he fired her. Steffy enlisted Liam's help to prove she had nothing to do with the doctored video. Taylor believed Steffy's claims of innocence, and she proved it by signing over her 25 percent of Forrester to Steffy.

Bill expressed interest in purchasing Steffy's shares, but she was determined to clear her name first. Liam informed Ridge that Justin had sabotaged the tribute, and Ridge pleaded with Steffy for forgiveness. Steffy returned to Forrester, and she and Stephanie worked together to force Brooke to take a leave of absence. Steffy became intrigued by Liam after she learned that he was Bill's son, but she was distracted by a PR assignment in the international office.

Steffy returned to L.A. several months later and immediately resurrected the feud between the Forresters and the Logans. She also indicated a renewed interest in Bill. She innocently stopped by the cliff house and found Amber dangling from the balcony, moments after Steffy had seen Bill rush off. Steffy pulled Amber to safety, and later, Bill confided to Steffy that he had been willing to murder Amber, but her fall had been an accident. Katie overheard and was disgusted with Bill, and Steffy used the couple's rift to make inroads with Bill.

When Thomas and Brooke's return flight from Australia vanished from the radar near Fiji, Steffy turned to Bill for help. He offered his private jet and accompanied Steffy, Ridge, and Taylor on an excursion to attempt to find the missing duo. When they found out that Thomas and Brooke were alive, Steffy flew into Bill's arms and proclaimed her love for him. They were both startled when he spontaneously returned the sentiment. Steffy was not happy when Bill reunited with Katie upon their return home.

Steffy was elated when Taylor asked her to be maid of honor at Taylor's remarriage to Ridge, but her dreams to reunite her family were crushed when Stephanie halted the wedding and confessed that she had bribed Thomas to lie that he and Brooke had slept together. Steffy felt abandoned when Ridge reunited with Brooke, and she turned to Bill for comfort. Steffy and Bill couldn't deny their attraction, and he promised to leave Katie, but his plans went awry when Katie surprised him with a vow renewal ceremony in front of their friends and family. Undeterred, Steffy purchased Jackie and Owen's penthouse to use as a love nest, and she befriended Liam.

Steffy was devastated when Bill decided to stay in his marriage after Katie suffered a heart attack. While preparing a bath, Steffy slipped, hit her head, and fell into the tub, unconscious. Liam rescued her when he stopped by to return Bill's keys. She impulsively kissed Liam, and the pair bonded over Liam saving her life. She planted seeds of doubt in Liam's mind regarding Hope's commitment to him.

Steffy and Liam spent time together as friends, though she made it clear she wanted more, and Bill encouraged her efforts to pursue Liam. Steffy and Liam kissed on the night of his bachelor party, and when Hope spied the buss, she abruptly ended their engagement without explanation. The same night, Liam asked Steffy to marry him, and after she accepted, they made love.

Bill sent Liam and Steffy to Aspen on his private jet. Hope reconsidered her decision and chased after them to tell Liam she still loved him. Steffy learned of Hope's presence in Aspen and orchestrated a surprise wedding at the top of Ajax, and Hope was forced to watch the couple marry while she was trapped in a gondola, which Steffy had ordered Bill to stop. Liam later confronted Steffy regarding the incident, but she denied any wrongdoing.