Id Software practically invented the genres that would define the PC as a gaming platform. They started out with the first-person shooter in Wolfenstein and then followed that with online multiplayer in Quake.
It's difficult to think of another games company that established so many famous gaming names in such a short space of time, as id sped from Wolfenstein, to Doom and to Quake. But after producing three Quake games in just four years things went quiet. In fact, id have only released one game in the past nine years - Doom 3. At long last they're on the verge of returning.