Chell awakens from stasis at the Aperture Science Enrichment Center and must use portals to escape testing and defeat the evil AI GLaDOS. She encounters two other main characters - GLaDOS, a murderous computer who runs the tests, and Wheatley, a bumbling but manipulative personality core. Chell is a highly determined and intelligent test subject who works to outwit GLaDOS and Wheatley using her wits and ability to manipulate portals to gain her freedom from the facility.