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.
ShadowCaster
The "ShadowCaster" game engine, a successor of the "Wolfenstein 3D" engine and a predecessor of the "Doom" engine, was written by id Software's John Carmack and licensed to Raven Software. Carmack wrote the "ShadowCaster" 3D engine during his technology research after id Software completed "Wolfenstein 3D". The engine features diminished lighting, texture-mapped floors and ceilings, walls with variable heights and sloped floors. The engine was "about half as fast as that of "Wolfenstein"" but fit the exploration of "ShadowCaster" rather than the fast-paced action of "Doom".