The original "Team Fortress" was developed by Robin Walker and John Cook. This early version of "Team Fortress" was a free mod for the 1996 PC game "Quake". In 1998, Walker and Cook were employed by Valve. At the time, Valve just released its first game, "Half-Life." Valve began developing "Team Fortress 2" as a separate retail game using one of Valve's own game engines, GoldSrc. In 1999, Valve released "Team Fortress Classic," a port of the original "Team Fortress," as a free "Half-Life" mod. "Team Fortress Classic" was developed using the publicly available "Half-Life" software development kit as an example to the community and industry of the flexibility of the "Half-Life" game.