It's a slightly sad quirk of video game history that id Software's Wolfenstein 3D is lauded as a masterpiece of gaming while the title it was heavily inspired by - name and all - is afforded no such honour.
Yet id's comic blaster owes everything to a stealth game released in 1981 called simply Castle Wolfenstein.
The game was developed by now-defunct Muse Software, with much of the work being done by Silas Warner, a literal giant in the field of game development (Warner was 6'9").
Castle Wolfenstein is in many ways a precursor to Metal Gear, in that it was played from a top-down perspective, and emphasised exploration and stealth at the expense of balls-to-the-wall action (though there was still killing to be had if you felt like using some of the game's rarest commodity, ammunition).
You played a prisoner in said Castle Wolfenstein, who upon busting out had to find some Nazi war plans then make your way out to freedom. The castle was made up of around 60 individual rooms, or "levels", with many of them featuring both Nazi guards and, more impressively, destructible environments, with interior walls able to be wiped out by explosive devices.
While Castle Wolfenstein was notable for all of the above, along with the fact it included actual lines of digitised speech (a rare treat in 1981), what's more interesting is how much it influenced the development of id's shooter over ten years later.
Not only did id lift the name (there was no actual Castle Wolfenstein, but because Muse had let the original game's rights lapse, id were free to use it as a title), it paid homage to the overall premise of the game, and even recreated the original's opening: in the 1981 game, you begin in a prison cell with a pistol, just like you do in Wolfenstein 3D.
Castle Wolfenstein was followed in 1984 by Beyond Castle Wolfenstein, which this time works in reverse, as you had to infiltrate a Nazi bunker (as opposed to escaping from one) and kill Adolf Hitler. Aside from the change in setting, gameplay and graphics remained largely the same.
Both games ended up being released on the Apple II, Commodore 64, Atari and PC. Sadly, their creator Silas Warner passed away in 2004 following a long battle with kidney disease.