Team Fortress (TF) is a team- and class-based multiplayer online first-person shooter video game mod based on id Software's Quake Engine, and later QuakeWorld Engine. Team Fortress, also known as Quake Team Fortress (QTF), and later QuakeWorld Team Fortress (QWTF), was designed and written by Robin "Bro" Walker, John "Jojie" Cook, and Ian "Scuba" Caughley in 1996. Because of its popularity, it has spawned an endless amount of mods for not only Team Fortress, but other games as well. Valve took an interest in the Team Fortress Software organization and hired the three creators to work on a Team Fortress Half-Life mod, and later a standalone version called Team Fortress Classic (TFC), released in 1999. A standalone sequel to Team Fortress Classic, Team Fortress 2 (TF2), was developed by Valve and released in 2007.