Wheatley

Wheatley is the true main antagonist of Portal 2. He is a personality core who initially appears as the player's friend and guide, and speaks in a non-robotic British accent that sounds very much like an actual person rather than a fictional character. At the beginning of the game, Wheatley awakens Chell, who has been in stasis for several years, and tries to help her escape the Aperture Science facility, but is destroyed by GLaDOS when she is accidentally reactivated. Despite being killed, Wheatley reappears later and helps Chell defeat GLaDOS by replacing her program in the main control system with him.

But right when Wheatley is about to let Chell go free, he turns evil and betrays the player, accusing them of selfishly using him. He traps GLaDOS in a potato battery, and she recognizes his voice as a program the scientists once installed into her that gave her terrible ideas in an attempt to slow down her rise to power. Infuriated, Wheatley breaks the escape platform and throws them both into an extremely deep shaft leading to the lowest areas of the facility. As they fall, GLaDOS explains that Wheatley was designed by the scientists to always come up with bad ideas (in her own words, to be a "moron").

When Chell makes her way back to the main facility with GLaDOS, Wheatley has redesigned all the test chambers in his own image, combining the turrets and companion cubes into one and even changing the logo on the loading screen to "Wheatley Laboratories". However, as he is designed to make bad decisions, these changes have also put the facility at risk of a nuclear meltdown. When they encounter him on a screen, GLaDOS tries to stump Wheatley by asking him a paradoxical question ("Is this statement false?"), but that does not work. Eventually they reach the core chamber again, where Wheatley states he has been studying the final boss fight from the first game and has changed all the things that allowed GLaDOS to be defeated then, but despite this Chell is still able to corrupt and replace his personality cores and is about to press a button that will replace his program with GLaDOS, but Wheatley reveals that he had booby-trapped the button and it explodes, injuring Chell and blasting a hole in the ceiling revealing the Moon in the sky. Chell shoots a portal up to the moon which sucks everything onto its surface, where GLaDOS reaches out to save Chell and launch Wheatley into the vacuum of space.

After the credits, Wheatley is seen floating in space along with one of his personality cores, who is obsessed with space, where he laments his fate and says that he feels genuinely sorry.