The body of Gordon Freeman from the Half-Life series can be found in the Wild Territory area. Searching his body, it's possible to find his PDA. In it, he mentions both Black Mesa from the first Half-Life title, and "some strange town in Russia" (most likely being City 17 from Half-Life 2), and how he had to sell his crowbar for a can of meat. Next to him is a crate with a Desert Eagle called "Big Ben." This could ether be a reference to the famous clock tower of the same name in London, or, since it is near Gorden's body, a reference to Half-Life's creator, Gabe Newell, specifically his nickname, Gaben.

An early build of the game, specifically build number 1114, used animations and sounds from the Valve title "Counter-Strike".