The Aperture Science CEO whose recordings appear in Portal 2 is Cave Johnson.
Johnson founded Aperture Science, the fictional research company whose underground laboratories provide the setting for the Portal games. In Portal 2, Chell discovers recordings of him while exploring abandoned testing areas built during earlier eras of the facility. The messages reveal Johnson’s personality: boastful, impulsive, competitive, and increasingly desperate to keep Aperture relevant.
The recordings also explain the company’s decline. Aperture’s test subjects changed from astronauts and war heroes to paid volunteers, homeless people, and eventually employees. Johnson’s health deteriorated after exposure to moon dust, which was used in the development of portal-conductive surfaces. His assistant Caroline later becomes central to the origin of GLaDOS.
A common mix-up is choosing Caroline or GLaDOS. Caroline was Johnson’s assistant, while GLaDOS is the artificial intelligence connected to her personality. Wheatley is a personality core voiced by Stephen Merchant, not Aperture’s CEO. Cave Johnson is voiced by J. K. Simmons.