Released on December 10, 1993, Doom was a first-person shooter developed by id Software for MS-DOS. Programmed by John Carmack with design by John Romero, it introduced networked multiplayer deathmatch mode and a modular WAD file system that enabled user-created content. Distributed via shareware, the first episode reached an estimated 15 to 20 million players within two years. Its engine advanced 3D rendering beyond id's earlier Wolfenstein 3D and established design conventions adopted across the games industry.