Computer tech Liam Cooper arrived in Los Angeles following the death of his mother, Kelly Cooper, who said he could find his father at design house Forrester Creations. Ridge Forrester denied knowing Kelly, but his brother, Thorne Forrester, had dated her; Bill Spencer, Jr. had as well, so Liam's potential fathers agreed to a DNA test. Liam was less than thrilled to confirm that barracuda Bill was his father, but Forrester ingenue Hope Logan helped him make the adjustment, which led to a sweet romance. Ridge's daughter, Steffy Forrester, also expressed an interest in Liam, but Liam wasn't interested.
Liam got drunk after a misunderstanding with Hope and was taken home by social climber Amber Moore. Liam fell, suffering a concussion when he hit his head, and therefore couldn't remember if he and Amber had made love, as she claimed. Amber soon told Liam that she was carrying his baby, leading to Liam and Hope breaking up and making up with dizzying frequency as they tried to decide what was best to do for Liam's unborn child. Liam's relationship with Hope was also threatened by Hope's ex-boyfriend, Oliver Jones, who wanted to win Hope back. While helping Amber light a pilot light in her mother's trailer, there was an explosion that caused Liam to have a second concussion. Months later, when Amber gave birth to an African-American baby, Liam realized he had been duped by Amber and reached Hope with the news just as she was about to say yes to Oliver's marriage proposal.
Liam became frustrated when Hope wanted to remain a virgin until her wedding night, so he publicly proposed at the showing for her fashion line, Hope for the Future. Steffy, who had been rejected by Bill, slipped in her bathtub; Liam saved Steffy from drowning, and Steffy fell for him, letting him know that she was sexually available, since Hope wasn't. Liam was confused when Hope broke up with him via cell phone message and left her engagement ring on his mantel; he didn't know that Hope had seen Steffy kissing him, so he offered Hope's ring to Steffy instead.
Bill, who felt Hope wasn't good enough for his son, sent Liam and Steffy to Aspen, where Steffy surprised Liam with a mountaintop wedding. Liam later found out that Hope had followed him to Aspen to make things right, but couldn't because Bill had trapped her in a gondola, where she was forced to witness Liam's wedding. Despite being married to Steffy, Liam kept thinking about Hope, so Bill had Steffy bring Liam to Cabo San Lucas. Ironically, Steffy's brother, Thomas Forrester, who was interested in Hope, took Liam to the same resort. Despite Steffy and Thomas' best efforts to keep Liam from seeing Hope, he did spot her on the beach and gave chase on an ATV; Steffy followed but was injured falling off the vehicle.
Liam wanted to return to Hope, but felt obligated to stay with Steffy when she was diagnosed with a brain clot that could worsen under stress. Liam forgave Steffy for working with Bill in Aspen and Cabo, but was shocked when Bill's wife, Katie Logan, came to Liam and revealed that Bill had faked Steffy's MRI to manipulate Liam into staying with Steffy. Liam asked Steffy for an annulment, but his wedding to Hope was stopped when Steffy refused to sign the papers in favor of holding out for a proper divorce.
Hope relaxed her stance on waiting for marriage and moved in with Liam, but Liam was dismayed when Hope froze up in bed. A disgruntled fan of Hope's snapped a photo of Liam and Hope in public, causing the media to brand Hope an adulteress, since he was still legally married to Steffy. Liam seemed oblivious to Hope's increasingly erratic behavior, but after he saved from nearly drowning in the Forrester pool, she admitted to taking antianxiety medication, which is how she was finally able to make love to Liam. Hope promised to give up the pills, but when she hurt Steffy by crashing into her on the slopes of Aspen while strung out, Liam was furious and tended to Steffy. When Steffy relented and signed Liam's annulment papers, Liam tore them up.
Hope's mother, Brooke Logan, found out what Liam had done, but agreed to stay quiet, instead planning a wedding for Liam and Hope in Puglia, Italy. The day of the ceremony, Hope was a no-show, and Liam found a note saying she couldn't go through with it. Liam kissed Steffy and told her he loved her; he was about to take Steffy back to Los Angeles when Hope arrived, explaining that she had been delayed by the surprise appearance of her estranged father, Deacon Sharpe. Liam married Hope anyway, but continued to be conflicted about Steffy. Later, Hope saw video footage of Liam kissing Steffy, which Liam had accidentally recorded with his iPad. Hope refused to sign the papers that would legalize their marriage, instead insisting on a "do-over" wedding. The night before, Steffy "kidnapped" Liam to a club to show him how fun life with her could be, and, when a hungover Liam arrived for his wedding sporting dyed hair and a tattoo, Hope wanted nothing more to do with him, especially after hearing that he had kissed Steffy at the club.
Liam found his way back to Steffy, and they moved in together. But their idyll was rocked by several revelations: not only had Hope's brother, Rick Forrester, gotten his DJ friend, Othello, to lie that Liam had kissed Steffy the night before his wedding to Hope, but Bill had bribed a warden to spring Deacon from a prison in Genoa City, Wisconsin for the express purpose of sabotaging Liam's Italian wedding. Liam punched Rick, then disowned Bill, who stabbed himself in the chest with his sword necklace. The shocked Liam recanted, unaware that Bill had only stabbed himself in his money pouch in an effort to further manipulate Liam.
Liam was intrigued when Hope became determined to win him back. Steffy saw Hope kissing Liam, so she took a business trip and told Liam he needed to get Hope out of his system. Liam wanted time to think, but Brooke surprised him and Hope with a wedding. Liam got caught up in the moment and nearly put a ring on Hope's finger, but Steffy arrived and admitted she was carrying his child. Liam ultimately chose to make a home with Steffy and the baby, and soon married Steffy in an outdoor ceremony that included Steffy riding up the aisle on a motorcycle. Liam asked Steffy to give up riding until after the baby was born, but, anxious to get around a traffic jam and get home to Liam, Steffy rode anyway and was in an accident that killed their baby. Liam was angry, but Bill encouraged Liam to vent at him rather than further upset the grieving Steffy, who had slid into a deep depression.
Liam was thunderstruck when Steffy suddenly announced she was moving to Paris alone, declaring he should reunite with Hope. Liam couldn't move on without answers; he eventually flew to Paris and discovered that a botched D&C procedure after the miscarriage had rendered her infertile. Liam wanted Steffy to come home, but she refused, so Liam proposed to Hope, who had since become interested in Wyatt Fuller. Bill became Liam's roommate when Bill ruined his marriage to Katie Logan by sleeping with her sister, Brooke. But Liam was shocked to discover that he had a half-brother in Wyatt, since Wyatt's mother, Quinn Fuller, had a teenage fling with Bill.
Liam wanted to welcome Wyatt as his brother, but thought better of it when Wyatt kissed Hope. Liam punched Wyatt, and took Bill's side when Bill threw Wyatt out of the family for challenging Bill's affair with Brooke. Again having to wait to marry Hope until his divorce from Steffy was final, Liam invited Hope to move in with him. However, Liam was unhappy when Hope inadvertently selected Quinn's company, Quinn Artisan Jewelers, to design accessories for Hope for the Future (now HFTF), which meant Hope would be working with Wyatt. When Wyatt told Liam that Hope was fair game until she was married, Liam got Steffy to agree to an annulment after all.
Not thrilled when Hope had to travel to Mexico with Wyatt on business, Liam made one video tribute for Hope, and another one for Steffy, as a way of saying goodbye. Hope received Steffy's video by e-mail and broke off her engagement to Liam, but Liam discovered that Quinn had gotten into his tablet and forwarded the video to Hope to push her toward Wyatt. Hope admitted that Liam's discomfort with Wyatt was karma for Liam having waffled between Hope and Steffy; soon, Liam got tired of waiting and gave Hope an ultimatum about marrying him. Hope agreed to become Liam's wife, but, on his wedding day, Steffy visited from Paris to tell him that a new procedure now allowed her to have children. Liam was happy for Steffy, but said his future was with Hope; unfortunately, Hope saw them in heavy conversation and took off for Hawaii with Wyatt.
When Liam discovered that Quinn had brought Steffy to town to stop his wedding to Hope, Liam went to Hawaii to explain Quinn's sabotage. Liam was disappointed when Hope accepted his explanation, but sent him back to L.A. alone. Though Hope decided to date Wyatt, Liam still felt his half-brother was bad news, and stumbled upon security footage that showed Wyatt pocketing a rare diamond on loan to HFTF, then planting it on real jewel thieves who had come to steal the gem. Quinn trapped Liam in an elevator to keep him from exposing Wyatt, but Liam escaped and crashed Hope and Wyatt's camping trip on the beach. Hope ditched the bickering brothers once she learned of Wyatt's "theft", but Hope forgave Wyatt and stayed with him, while Liam remained oblivious to the crush that young Aly Forrester, Hope's childhood friend and "shadow" at Forrester, had developed on him.
Liam was thrilled when Katie, who had seized control of Spencer Publications in her divorce from Bill, promoted Liam to vice president. Liam encouraged Katie to act on her feelings for Ridge, who was on the fence about remarrying Brooke. Later, Liam was alarmed to hear loud noises and breaking glass coming from Bill's room, and accidentally walked in on Bill and Quinn having raucous, S&M sex. But, hearing that Hope had had a pregnancy scare with Wyatt, Liam lured Hope to Wyatt's camper and drove off with her inside to convince her they'd almost lost their chance to be together. Liam asked Hope to consider dating both him and Wyatt, or he would move on permanently. She did, and Liam was pleased when Hope adopted a kitten at an animal shelter they visited.
Liam tried to relax in the Forrester steam room, but Quinn, wanting Liam to stay away from Hope, trapped him inside and cranked up the heat. Then, Liam found out that Ridge had gone to Abu Dhabi to stop Bill and Brooke's wedding, but only after Quinn showed Ridge a photo of her and Bill in bed together, leading to Ridge going missing after falling out of a helicopter; Liam called Quinn a "vile, manipulative, evil bitch," which got him punched by Wyatt. After witnessing the violence, Hope chose Liam, but Quinn became more threatening after Forrester terminated their contract with Quinn Artisan Jewelers: Quinn blamed Liam and stabbed him in the throat with his sword necklace during an argument. During a windy night, Liam heard something banging around his house and was sure that Quinn was terrorizing him. Liam stumbled in the dark and fell, spraining his ankle.
When Quinn returned and threatened to kill him and Hope, Liam went to Wyatt, who wanted to wait on calling the police until he had a chance to talk to his mother. But Quinn attacked Liam and kicked him in his injured ankle; she was just about to impale him with a sword when Wyatt ran in and stopped her. Liam and Wyatt decided not to call the cops on her, and bonded as brothers over the ordeal. Liam asked Wyatt to be his best man at his wedding to Hope, but Liam became upset when Wyatt gave Hope the HFTF diamond, which he had inherited from its owner. Though Hope insisted that she was only accepting the diamond for the sake of the company, Liam walked out on her.
Hope had to travel to Paris for a photo shoot involving the diamond, and asked Liam to meet her at a specified time in front of the Eiffel Tower so they could be married; if he didn't show, she would know their relationship was over. Aly Forrester teamed up with Ivy Forrester, who came from Australia to replace Quinn as a jewelry designer, to convince Liam to make the trip to Paris. Ivy flew there with him, and encouraged him to run on ahead to the Eiffel Tower while she sat on the bridge of the River Seine to take pictures of his reunion with Hope. But Liam heard a scream behind him: Ivy had fallen into the river, so Liam jumped in to save her. Once he was sure Ivy was all right, he made it to the Tower, only to find that Hope was gone.
Liam and Ivy ran to the offices of Forrester International to find Hope, and learned that Hope had flown to Monte Carlo with Wyatt; Liam was devastated when Bill called to confirm that Hope and Wyatt had been married on his yacht. Liam chafed when Bill ordered him to come to the party celebrating the marriage and congratulate the bride and groom, and, when Bill publicly put Liam on the spot, Wyatt saved him by changing the subject. Over Bill's objections, Liam got Hope alone and told her that he had just missed her in Paris, but Hope insisted she was married to Wyatt now.