Wheatley, referred to as an Intelligence Dampening Sphere by GLaDOS, is a loose Personality Construct and a main character in the single-player campaign of Portal 2. He was one of the many cores seen awakening at the end of Portal.
Of masculine programming and in possession of an English West country accent, he is Chell's sidekick and guide during the first half of the game, but eventually becomes the game's main antagonist having been mad with power.
According to GLaDOS, Wheatley was originally designed by the Aperture technicians as an "intelligence dampening sphere". He was intended to render her less dangerous by forcing upon her the most idiotic ideas, therefore hampering her decision-making process. Wheatley states that, at one time he almost got a job in the manufacturing department, but the foreman instead chose an "exact duplicate of himself". The only known duty that Wheatley has over the Enrichment Center is what he considered the "least desirable job available": attending to the "smelly humans" in the Extended Relaxation Center.
Wheatley is talkative and friendly at first, although his main motivation in befriending Chell seems to be obtaining her help in escaping. He frequently second guesses his own decisions and is not especially assertive, always trying to persuade Chell to go along with his plans rather than demanding that she do anything. Despite his general indecisiveness, he shows initiative in seeking out Chell to act on his escape plans. He is patient and, when his actions lead to unpleasant consequences, he is quick to take responsibility and apologize - although usually as a lead-in to asking Chell to go along with another of his plans. However, his apparent friendliness is at least partially a ruse from the beginning. A few stray comments early on reveal that his true attitude toward humans is mildly contemptuous, and at the end of the game, he reveals that he fully expected Chell to be killed all along, as several previous human test subjects with whom he tried to escape had been.
Once he takes over the Enrichment Center, his stupidity becomes more apparent. He crudely attaches turrets to weighted cubes to create self-guided cubes as an ill-conceived replacement for human test subjects, then tries to correct their deficiencies by shouting at them; he ignores signs of an imminent reactor core meltdown, shutting the alarms off rather than addressing the problem; he can only manage to build absurdly simple test chambers, such as a button which drops a cube onto another button when pressed, except when he steals ideas previously implemented by GLaDOS; and when he attempts to imitate GLaDOS' methods of antagonizing her test subjects, the best insult he can come up with is "fatty fatty no-parents." GLaDOS generally finds it easy to goad and manipulate him - except when he manages to foil her by not being smart enough to spot the bait; when she presents him with a simple logical paradox which she says will disable any AI and even affects the "Frankenturrets," he survives by failing to even notice the contradiction. He seems profoundly insecure about his intellect, reacting with fury whenever GLaDOS refers to him as a moron.
In contrast to his general lack of intelligence, however, Wheatley occasionally manages to come up with genuinely clever ideas. After GLaDOS puts Chell back into testing, he successfully rescues her. He correctly identified the defenses that would need to be shut down before confronting GLaDOS, although he has no plan for actually doing so. Perhaps most impressively, he manages to trick both Chell and GLaDOS by rigging an Aerial Faith Plate to send them flying in the wrong direction so that they land in a death trap. Finally, when Chell reaches his lair, he has the room set up to counter every trick Chell used to defeat GLaDOS before, even rigging the stalemate button to explode when she reaches it.
Once attached to GLaDOS' mainframe, Wheatley begins to display an increasing degree of paranoia and resentment toward Chell. Goaded by GLaDOS, he betrays Chell almost immediately after their victory, claiming that he grew tired of doing all the work while she ordered him around (in fact, the situation was almost exactly the opposite). During the final boss fight, he complains that Chell maliciously chose not to catch him when he detached himself and deliberately deceived him by not telling him she was the one who defeated GLaDOS; furthermore, he says, Chell never wanted to share in his success. He also suggests that Chell and GLaDOS were allied against him from the beginning.
After his defeat and disconnection from GLaDOS' "body," however, he expresses remorse for his actions and says he wishes he could apologize to Chell.