The player plays as a woman named Chell who has to go though tests while being watched by a computer named GLaDOS, an acronym for Genetic Lifeform and Disk Operating System. GLaDOS provides all of the game's dialog and is known for being clever, funny, and sarcastic, promising the player character a cake if all of the tests are finished. GLaDOS and the testing rooms were created by a company called Aperture Science, which competes with Black Mesa. The player must use a gun, called the Portal Gun, that makes two linked holes, called portals, to solve puzzles. The two portals, one blue and one orange, are linked together and let the player get from one place to another. When the player enters the blue portal, they will come out of the orange portal. When the player enters the orange portal, they will come out of the blue portal.