Wolfenstein
The "Wolfenstein" series of video games started with the 1981 stealth-adventure video game "Castle Wolfenstein". It was developed by American programmer Silas Warner, a pioneer in the early eras of video gaming, especially the stealth genre. It was published by his (then) company M.U.S.E. Inc. (Muse Software). The player controls an unnamed American prisoner of war as he steals war files containing information about secret German war plans while avoiding or sometimes killing guards, and tries to escape the fortified Nazi stronghold Castle Wolfenstein, set during World War II. The game is often credited as one of the first video games of the stealth genre, since it focuses more on avoiding or disarming enemies, and killing them is considered a last resort.
Wolfenstein 3D
"Wolfenstein 3D" was a critical and commercial success, garnering numerous awards and selling over 200,000 copies by the end of 1993. It is widely regarded as having helped popularize the first-person shooter genre and establishing the standard of fast-paced action and technical prowess for many subsequent games in the genre, as well as showcasing the viability of the shareware publishing model at the time. FormGen developed an additional two episodes for the game, while Apogee released a pack of over 800 fan-created levels. Id Software never returned to the series, but did license the engine to numerous other titles before releasing the source code for free in 1995, and multiple other games in the "Wolfenstein" series have been developed by other companies since 2001.