Half-Life is a series of video games created by Valve Corporation. The player plays as a character named Gordon Freeman, who is a survivor of a terrible accident at the Black Mesa Science Research Company. A group of scientists make a portal to another dimension, and accidentally let in many alien monsters that start killing everyone.
A related game, Portal, was released in 2007 and takes place in the same universe. Portal, Half-Life 2, Half-Life 2: Episode One, Half-Life 2: Episode Two, and Team Fortress (an unrelated game) were put together into one package for sale in 2007. This package is known as The Orange Box.