Wolfenstein is a series of World War II video games, originally developed by Muse Software. The third game in the franchise, Wolfenstein 3D, was developed by id Software, and is widely regarded to have helped popularize the first-person shooter genre. In 2001, the series was rebooted with Return to Castle Wolfenstein, developed by Gray Matter Interactive. This was followed by Raven Software's Wolfenstein in 2009, and MachineGames' in 2014 and in 2015.