Portal 2 is a puzzle-platform game developed and published by Valve Corporation. It is the sequel to the original Portal game, and follows the story of a test subject named Chell who must use her portal gun to escape the Aperture Science labs and confront the facility’s malevolent artificial intelligence, GLaDOS. Portal 2 is known for its expanded gameplay, which introduces new mechanics such as gels that can alter the properties of surfaces, and its improved graphics and level design. The game also includes a cooperative multiplayer mode, in which two players must work together to solve puzzles and escape the labs. Portal 2 was released in 2011 and was well-received by critics and players, who praised its challenging and innovative gameplay, as well as its humorous writing and characters. It has since been re-released on multiple platforms and is considered one of the best games in the series.