The Infinite Space

A small spherical robot of approximately forty centimeters in diameter. He has a single blue optic with a large crack through its middle. Unless carried or attached to an outside mechanism, he is incapable of moving much more than wriggling about. He has a periodic twitch that sends out occasional sparks.

If in a human/android body, he's a scrawny man who appears in his late thirties or early forties. He's below average in height, with thin dirty blond hair and badly cracked glasses.

Wheatley talks like breathing. He talks instead of breathing. He has no brain to mouth filter, and lives by the hope that if he says enough things fast enough no one will pick up on the detail that he has no idea what he's talking about. It hasn't worked yet but maybe it will soon.

As a robot designed to make others fail, he craves to be useful and belong but is constantly braced for rejection. He overcompensates by blaming others wherever possible and refusing accountability. If he never admits fault no one can be mad at him, probably. Better for him to accuse others of being the problem before they can turn on him.

Wheatley's conflicting desires for approval vs paranoid self-protection combine with his constant prattle to make a robot with a wildly mercurial temperament. His mood will flip at the slightest provocation, and depending on the wind his thoughts can and will contradict within the same sentence.

Pre-Canon.
The Intelligence Dampening Sphere was designed by Aperture Science Laboratories in an attempt to stop GLaDOS, the AI who controlled the facility, from killing everyone inside. The IDS' purpose was to generate constant chatter, distracting and lagging out GLaDOS' system--in her words, he generated terrible ideas to turn her into an idiot.

After he failed to sufficiently kerb her bloodlust, the IDS was bounced around to various departments of Aperture, where he routinely failed any task given to him. Finally, he was left as attendant to the Relaxation Center, watching over comatose human test subjects.

Portal 2, Chapters 1-5
Upon realizing A) all the humans he'd been left in charge of had gone braindead and B) the reactor core of the facility was en route to a meltdown, the IDS (having renamed himself Wheatley) woke up the one surviving human subject in hopes that she could help him escape before everything exploded.

In order to get past GLaDOS, the human plugged Wheatley into the Aperture mainframe to put him in charge of the facility and strip Her of power. Wheatley proceeded to immediately go mad with power and paranoia.

Chapters 6-9
Wheatley quickly became addicted to Testing Euphoria, a programmed high that rewarded successful scientific experimentation. In his obsession with reaching this high he neglected to pay attention to basic needs of the facility, up to and including the reactor core's imminent meltdown. He attempted to use his former partner for testing, eventually ramping up to outright attempted murder as his frustration and paranoia peaked.

In the course of their battle for survival the human opened a portal onto the moon, through which Wheatley was sucked into the vacuum of space and left to float in orbit indefinitely. Cut from the addictive power of the chassis he quickly realized his mistakes, just in time to think about them for the rest of his lonely digital life.

Physical Affection.
Wheatley craves touch but is also confused and easily overwhelmed by it. He'll likely respond with discomfort if touched unexpectedly.

Physical Violence.
Kick his ass, he deserves it. No killing.

Relationships.
Like physical contact, he craves relationships but is also made uncomfortable by them. He wants to be liked but will push people away for getting too close. Whatever kind of relationship, expect some hot-and-cold responses.

Abilities & Powers.
He makes other robots worse by overloading them with inane chatter. Also he has a flashlight.