Gilbert Lawson served as Cornelius Hawthorne's personal assistant for more than 30 years. After Cornelius's death, Gilbert was made executor of his estate and invited Pierce and seven of his closest friends to a reading of the will. He explains that they are to compete in a video game for the inheritance that was left for Pierce. When Gilbert joins the game, he reveals to Pierce his true heritage and the personal stake he has in winning the inheritance for himself. His first appearance was in the Season Three episode "Digital Estate Planning". He is portrayed by actor Giancarlo Esposito.
In the study group's third year at Greendale, Jeff inadvertently caused Pierces father to have a heart attack which ended up killing him ("Advanced Gay"). Months later, Gilbert Lawson, acting as the executor of Cornelius' estate, directs Pierce to bring seven of his closest friends to a special location for the reading of his fathers will. The study group ends up accompanying Pierce to a warehouse owned by Hawthorne Industries where Gilbert greets them. He introduces himself as Cornelius' former assistant for the last thirty years and then over shares by mentioning how as a child he read the bible to Hawthorne while he bathed. Gilbert then explains the reason behind the mysterious instructions he gave them; Pierce's inheritance must be won by playing a video game, "Journey to the Center of Hawkthorne". Once the group starts playing the game, a virtual avatar of Cornelius appears and explains the rules encouraging them to fight each other for the prize. The group instead agrees to help Pierce win his inheritance.
However, their efforts are hampered by Gilbert who joined the game in the vacant eighth spot. Having superior knowledge of the game as well as cheat codes, he easily defeated the study group sending them back to respawn at the beginning of the quest. Frustrated by the continuous setbacks, Jeff and Pierce confront Gilbert in the real world for his obvious cheating. Lawson then reveals the reason he is competing for the inheritance and tells everyone know that he too is also Cornelius' son. He is the result of an affair Cornelius had with Pierce's former nanny Edda's hot cousin. He states he has just as much of a right to the money and that he was more of a son to Cornelius than Pierce ever was. While Pierce and Jeff return to the game and try to rally the rest of the group, Gilbert arrived at the games final stage where he encountered the Cornelius avatar. The program identified Gilbert and offered him the inheritance only if he signed a legal document that ensured he would never reveal his true nature of his relationship to Cornelius. Gilbert rejected the offer and the avatar attacked him. He was saved by the arrival of the study group and their new allies.
The Cornelius avatar then transformed into a giant monster to deal with them. The alliance managed to weaken him with powerful new weapons they had acquired but the avatar was still strong enough to eliminate most of them. Pierce then arrived at the scene riding on top of a large missile and engaged in a suicide run that destroyed the body of the avatar. With only the head remaining, the Cornelius avatar acknowledged he had been defeated. Pierce and the study group agree to forfeit the game and allow Gilbert to claim the reward feeling that he earned it for all the years he had to put up with the real Cornelius. Gilbert delivers the final blow to the avatar, wins the game and claims the inheritance. He then apologizes to the group for his behavior and proposed he make it up to them by taking them out to a bar called 'Skeepers" for margaritas. Pierce tells him he is happy to have a brother and unintentionally makes a racist comment. Britta tries to apologize on Pierce's behalf but Gilbert takes it in stride saying "it's okay, he's family." ("Digital Estate Planning").
The following year, Gilbert visited Pierce at his mansion to give him the deed to the estate. After entering the lace he noticed that it had fallen into a state of disrepair with not only the house but also the bills being neglected. After paying off the debt he decided to stick around and look after Pierce clandestinely. He lived in the mansion in secret for six weeks until Halloween. That day Pierce decided to throw an prank on the study group and told them he was trapped in the mansions panic room. When they arrived to try and free him, he used a series of elaborate tricks to scare them into believing the mansion was haunted by the ghost of his dead father. After revealing the hoax and taunting the group for having fallen for his gag, Abed shows him footage from the mansions surveillance cameras a few days ago. In the video, a shadowy figure watched him while he slept. Pierce vehemently declares that was not a part of the prank.
He immediately locked himself and the others in the panic room now believing himself that the mansion is haunted. The door to the panic room then opens and Gilbert finally shows himself. Pierce questions why he is in his house but is corrected by his brother saying the house is actually his. After telling him about his initial visit weeks ago, he explains that Cornelius' death last year affected him more than he realized. Looking to fill that void, he sought out Pierce and decided to look after him like he did with their father. He then apologizes to his half- brother for his actions and turns to go but is stopped by Pierce. He lets Gilbert know that he wouldn't mind having a roommate and would be okay with him moving in. Gilbert gladly accepts his invitation and the two brother embrace in a hug as the study group looks on approvingly ("Paranormal Parentage").