Team Fortress is a series of class-based First-person shooter video games, originally created by Robin Walker, John Cook, and Ian Caughley. Team Fortress was originally made as a mod of the game Quake, until it's rights were purchased by Valve, it's current owner. So far the series spans a total of 20 years, and features 3 official games in the series, as well as dozens of unofficial versions created as mods of other games.
What defines an "official" Team Fortress game is if it was developed in whole or in part by the game's original developers Robin Walker, John Cook, and Ian Caughley. After Valve's purchase of the series, the games have been primarily developed by Walker and Cook, with help and development by Valve's employees.
Team Fortress (1996)
The original Team Fortress, also known as Quake Team Fortress, was developed by John Cook, Robin Walker, and Ian Caughley in 1996 as a Modification of the FPS game Quake. Team Fortress introduced the games class based system, with all 9 original classes developed and released gradually through updates over the course of 1996 and 97.
Team Fortress Classic (1999)
Valve, a then popular video game development company after the release of their first award winning title Half-Life, saw the popularity of the series and requested John Cook, and Robin Walker to recreate the game on their personal Goldsource engine, for a store release. Walker and Cook accepted, and the game was released as Team Fortress Classic in stores in 1999 to popular success. The game was well received and featured new weapons, levels, and updated graphics and servers. The series helped propel Valve into it's status as a popular multi-successful title company, and gave them a great foot in the multiplayer video game market.
Team Fortress 2 (2007)
After the success of Team Fortress Classic, Valve set out to create a sequel just a few years later. However, due to Valve's juggling of other development projects such as the Half-Life series, and their Steam video game service, as well as a general misunderstanding of where to take the series and what to do for the new title, led the game into a rough 9 year gap between Team Fortress Classic and Team Fortress 2.
Finally in 2007, Team Fortress 2 was released in a compilation with 3 other Valve debut titles in the Orange Box for the Xbox 360. Though fans were confused with the games choice of graphics, the game was a success and was well received by gamers and critics alike. Team Fortress was later released as a stand-alone title for computer platforms a year later, where the game achieved super-star success.
Team Fortress 2 on it's computer platforms featured countless improvements over the Orange Box edition, with new guns, and a trading system. One of the games most successful additions was it's in game digital store, where players can purchase in game items with real money, released a year later. The game holds the title of best selling game on the Steam network. Due to the game's in-game store being so profitable to Valve, Team Fortress was made free-to-play in 2012.