Portal 2 (2011): The sequel that takes place an unspecified amount of time after the original.Portal (2007): The relatively short game that started it all, chronicling Chell's journey as GLaDOS guides her through a series of test chambers in the Enrichment Center.Officially published games in the series: The game features the protagonist Chell, a human who woke up as an unwilling test subject in the Aperture Science Enrichment Center, a research facility which has become completely abandoned, save for the personality of the insane central A.I. As the name implies, the core gameplay element of the Portal games deals with using a 'portal gun' to create doorway-type portals in order to solve physics based puzzles. Portal is a First Person Puzzle Platformer video game series created by Valve that takes place in the same universe as the Half-Life series.