Half Life

Half-Life (stylized HλLF-LIFE) is a series of first-person shooter games developed and published by Valve. The major installments feature protagonist Gordon Freeman, a theoretical physicist who battles an alien invasion. Two of these games, Half-Life and Half-Life 2, are full-length titles, while two more, Half-Life 2: Episode One and Half-Life 2: Episode Two, are shorter, episodic titles. A third episode, Half-Life 2: Episode Three, was scheduled for release by Christmas 2007, but is now described as vaporware. The first game in the Portal series, set in the same universe as Half-Life, was released in 2007.

At the Black Mesa Research Facility, physicist Gordon Freeman is involved an experiment that accidentally opens a portal to another dimension, Xen. Fending off hostile aliens and US Marines sent to cover up the incident, he helps scientists launch a satellite rocket and travels through a portal to Xen, where he destroys the Nihilanth, an alien entity. He is forced into a contract by the mysterious G-Man, who has been watching his progress.