Potato Sack is an alternate reality game (ARG) created by Valve and the developers of thirteen independent video games to promote the release of Valve's game Portal 2, in April 2011. Valve president Gabe Newell envisioned the game as a "Cross Game Design Event" in December 2010, and allowed the developers free rein to design the game using Valve's Portal intellectual property. The game, requiring players to find and solve a number of puzzles hidden within updates of the thirteen games, led to the opportunity for players to release Portal 2 about 10 hours earlier than its planned release by playing games under the pretense of powering up GLaDOS, the sentient computer from the Portal series. The ARG's theme of potatoes is based on plot elements within Portal 2, specifically that for part of the game, GLaDOS's personality module is run off a potato battery.