Doom is the legendary first-person shooter created by Id Software and released for DOS in 1993. It was Id Software’s follow-up to their genre-defining Wolfenstein 3D. This was the first game to popularize multiplayer for this genre.
Doom II is Id Software's follow-up to their award winning Doom. Published by GT Interactive, it was released for DOS in 1994, just one year after its predecessor. Unlike most sequels, this one is actually good.
Duke Nukem 3D is a sci-fi first-person shooter created by 3D Realms and published by GT Interactive Software for PC in 1996. The game is the sequel of Duke Nukem and Duke Nukem II, two shooters/platformers created by Apogee Software.