 The developers of Portal 2 initially envisioned it as a prequel to Portal set in the 1950s , long before GLaDOS took over the Aperture Science facility , with events set in motion when Aperture CEO Cave Johnson becomes trapped within a computer . Johnson would have led an army of robots , which would battle against the player to rise to power within Aperture . In June 2008 , based on information from a casting call website and leaked script samples , Kotaku reported that Valve was seeking voice actors to play Johnson , named him as an AI and identified the game as a prequel . Valve attributed this leak to an " overeager agent " . Following negative playtester feedback about the omission of Chell and GLaDOS , Portal 2 was re @-@ conceived as a sequel . The team returned to the idea of exploring parts of the facility from Aperture 's early days , and reincorporated Johnson through a series of recordings . 
