Wheatley first appeared at the introduction of the game. Wheatley having crushed Chell's relaxation center. Luckliy, Chell was the only one who ended during that time. In order to do so, he needs assistance from one of the test subjects, but they don't run out of cryogenic supply until even more centuries later.
Many centuries later, Wheatley decides to escape the facility. Prior to the events of Portal 2, Wheatley took control of the Extended Relaxation Center a place designed to keep test subjects in cryogenic storage before being released into the test chambers. A few years later, for unknown reasons, he was deactivated and put into the construct's storage. Wheatley first appeared in Aperture Laboratories as an Intelligence Dampening Sphere, designed to be attached to GLaDOS to make her behave by generating an endless stream of terrible ideas.
