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.
Return to Castle Wolfenstein
This gameplay was later reutilized in a full-fledged commercial game "" set in id Software's "Quake" universe. A semi-sequel called "Wolfenstein" was developed by Raven Software and id Software and published by Activision, and released on August 18, 2009. A sequel titled "" and a standalone prequel expansion titled "" have also been released in 2014 and 2015. The Old Blood references RTCW with characters with similar names and the X-labs being mentioned.