From Wikipedia:

Wolfenstein 3D is a video game that is generally regarded by critics and gaming journalists as having both popularized the first-person shooter genre on the PC and created the basic archetype upon which all subsequent games of the same genre would be built.^{[1][2][3][4][5]} It was created by id Software and published by Apogee Software. Released on May 5, 1992 for DOS, the game was inspired by the 1980s Muse Software computer games Castle Wolfenstein and Beyond Castle Wolfenstein.

In Wolfenstein 3D, the player assumes the role of an American soldier of Polish descent, named William "B.J." Blazkowicz, attempting to escape from the Nazi stronghold of Castle Wolfenstein. After the initial escape episode, the player carries out five other episodes also organized against Nazi operations. Throughout the game numerous armed guards, attack dogs, and mutant soldiers oppose the player. The buildings traversed contain health supplies in the form of food and medical kits, various treasures, and hidden rooms. There are four weapons (a knife and three guns) available throughout each episode for the player's defense.

Wolfenstein 3D was released as shareware, which allowed it to be copied widely. The shareware release contains one episode, consisting of 10 missions (levels). The commercial release consists of six episodes, which includes the shareware episode and its two subsequent episodes. Later releases included a three episode mission pack called "The Nocturnal Missions". Like the shareware episode, each commercial episode contains 10 levels, bringing the game to a total of 60 missions. The game was originally released on the PC and subsequently ported to a wide range of computer systems and consoles. The source code of the game was published by id Software on July 21, 1995,^[6] while the artwork data, music and software tools of the game remain under copyright.

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