id Software's 2D platformers were making "10 times" more money than its early FPS games, and Doom might never have happened if the studio followed the easy cash

Doom and Wolfenstein 3D may never have happened if a developer hadn't almost fallen out of his chair playing their poorly selling FPS Catacomb 3-D.

While Wolfenstein 3D is often considered the origin of popular FPS games before Doom then sent the genre into superstardom, neither were the first FPS that id Software made. Tank-based shooter Hovertank 3D was the studio's first dip into the genre, while Catacomb 3-D was the studio's first foray into a character-based FPS.

However, despite Wolfenstein and Doom becoming revolutionary titles that would define a genre, they might never have happened if id made more responsible financial decisions. id only made $5,000 on Catacomb 3-D – about "ten times" less than the studio's 2D platformer series, Commander Keen was making – but thankfully Adrian Carmack got a fright.

"One of my more cherished memories of making Catacomb was Adrian almost falling out of the seat when he turned around right in the face of a troll," John Carmack recalls in John Romero's documentary on the making of Catacomb 3-D (spotted by PC Gamer). While this could have simply been a funny memory of development, it actually proved to be more pertinent than you'd think.

"This is where we could tell we're starting to get it," John Carmack explained, adding, "This is the future of gaming, rather than looking at the little sprites moving around on the screen and maybe getting tense. But it was the sense of shock. That was the first moment that locked into my mind that we were really onto something in this new genre and style of play."

Adrian Carmack defended himself, saying, "It just automatically sucked you in visually. You couldn't help it," adding, "That was just one of the craziest things in a videogame I'd ever seen. We definitely knew that we'd found a new game style, a new game type."

And despite Catacomb not becoming a massive hit, Romero recalls "One night, we talked about how Catacomb 3-D was just the beginning of a new way to play games, and that the future was 3D." He adds, "Within an hour, we had decided what our next game would be: Wolfenstein 3D, the grandfather of first person shooters."

FPS legend John Romero says Doom is "one of the great privileges" of his life on the game's 32nd birthday