According to Wheatley, his original purpose was to oversee manufacturing, but was relegated to administer over the "smelly humans" after the position was filled. His primary means of travel is an electric rail, which he detaches from in order for the player to carry him about. He can interface with various control points in the facility, manipulating panels and even entire rooms. His blue eye-core doubles as a flashlight. Animator Richard Lord admits that the physical construction of a personality core like Wheatley is impossible to recreate in real-life. The rotating discs that comprise his face were inspired by rotating tape wheels found in early computers.
Wheatley shares a hostile relationship with GLaDOS, and is largely aware of her malicious tendencies. GLaDOS describes Wheatley as a "moron" designed to do "incredibly stupid" things. Evidently, he is foolish, clumsy, destructive, oblivious, and often an unintentional cause of danger for the player. Despite being a computer, he is an abysmal hacker, attempting to defuse passwords procedurally, essentially by guessing-and-checking. While searching for a switch to power an escape pod, he accidentally reactivates GLaDOS, and forges poorly-instrumented plans for overthrowing her throughout the game.
After the life-support systems in the suspension relaxation vaults are exhausted, Wheatley and the rest of the laboratory is restarted. With the player, Chell, awake after centuries in suspended animation, Wheatley attempts to help her escape from the laboratory. According to a commentary track, Wheatley attempted to escape with several other test subjects in the past, all unsuccessfully.
After successfully leading Chell out of the testing grounds, he guides her deep into the manufacturing facilities, causing widespread havoc to GLaDOS' supplies, including turrets and neurotoxic gas. Eventually, GLaDOS is rendered defenseless, and the automated laboratory systems detects her as corrupted, and in need of a substitute core. Wheatley volunteers and, with Chell's input, takes on GLaDOS' role as the computer mainframe. He is immediately driven mad with power and assaults both GLaDOS and Chell, thrusting them into the deepest caverns of the Aperture Science center.
With Chell and GLaDOS both in dire straights, the two form a makeshift partnership to defeat Wheatley. Once the duo makes their way back to the surface, they find that Wheatley has already begun unintentionally destroying the facility, and forging his own box-turret hybrids for the purposes of testing. Upon discovering Chell back in the laboratory, he forces her through his own test chamber (later through GLaDOS' reserved test chambers) in order to activate a euphoria-inducer hardwired into the computer mainframe. As the tests go on however, he feels the sudden rush from testing disappear, which pushes him to do more testing.
Eventually, he resolves to kill Chell and GLaDOS in a direct confrontation by crushing them with spikes. He fails at this and attempts to murder them by other means, all of which fail. Wheatley prepares for one final confrontation with Chell by studying what GLaDOS did wrong during the final boss fight in the first game but unsurprisingly fails. After being overloaded with corrupted cores and re-replaced by GLaDOS, Wheatley is portaled into space by Chell, where he resides in eternity with the Space Personality core. After the credits, he admits that what he did to Chell was wrong.
The concept of personality spheres accompanying the player throughout Portal 2 was devised as a means to include large amounts of dialog without the technical or time restraints associated with lip-syncing. The role of Wheatley was originally played by several different personality spheres throughout the game. The idea was later abandoned, as mentioned by a narration track, because it proved difficult for players to forge a bond with multiple, interchanging companions. Some of these left-over characters are featured as corrupted cores.
During the initial demos of the game at E3 2010, Wheatley was voiced by Valve animator Richard Lord. While Doug Lombardi noted that the audio was simply a placeholder for the demo, Lord's performance was very well-received, urging Valve to retain Lord's voice in the final game. However, it was later revealed at GamesCom 2010 that in the final game Wheatley would be voiced by British actor/writer Stephen Merchant, known mostly for his work with Ricky Gervais. Stephen reflected on his performance in this Kotaku article, where he admitted he found working on the game 'exhausting', but admitted he was 'very pleased by the response' that people had to his performance of Wheatley. His voice work was heavily applauded by critics and fans alike.
The Ap-Sap was a promotional item for another Valve game Team Fortress 2, that was given to Steam users who bought the Portal 2: Songs to Test By CD in the form of a promotional code. This item resembles the Wheatley character complete with a voice-over by Stephen Merchant. The name of the item is a portmanteau of Aperture and Sapper.
Wheatley also appears along with GLaDOS, Cave Johnson and numerous other Portal assets in the Portal 2 Add-on for LEGO Dimensions. GLaDOS and Wheatley are also part of the stock game's campaign.
Neither of these appearances are officially canon, though the LEGO Dimensions Add-on has a story that directly continues from the end of Portal 2.