After all the success we had with Wolfenstein and the Commander Keen games, there was huge speculation about what our followup would be. Someone even came up with an acronym for their own fantasy version of it: SPISPOPD, which stood for Smashing Pumpkins into Small Piles of Putrid Debris. And then someone actually made that game.

We started work on something new in January 1993, putting out a press release announcing all the revolutionary things it was going to do: we said we fully expected it to cause the biggest loss of productivity in the world ever.

Then one day we were playing Dungeons & Dragons at the Texas HQ of our company, id Software, like we had done for years. John Carmack, lead programmer, was Dungeon Master as usual. I got greedy trying to procure a magic sword and caused the entire world to be overrun by demons. Something just clicked. We all loved sci-fi, especially Aliens: it was a fast-action movie and id wanted fast-action games. So what if – instead of finding aliens, like in every movie in the world – a player opened up a portal to hell? Your character, a space marine on a Martian base, would then have to fight all the demonic monsters pouring out.

First-person shooter games became huge because players could identify directly with the character, but early versions had to be designed around limited speeds. The advent of Intel's 386 microprocessor finally gave us more horsepower: we could start making stuff move fast. Carmack put in as many new features as possible: irregular walls, sloping floors, changing light levels. The aim was to be cool and realistic – but also fast. We wanted to make it the most fun thing we could ever think of playing. There can't be a more fun game in the world.

I wrote the programme behind all the levels, and did a lot of the design and audio work. The artists kept Necronomicon, a book of images by the Swiss surrealist HR Giger, open in front of them, to help them come up with crazy disturbing stuff. That's why we have walls that are like spines and screaming faces, and marines impaled on spikes. It inspired hellish monsters, too, like the cacodemon – the one that flies, shoots lightning and then spills its blue guts out when it dies. It looks very cartoon-like today, but it was the coolest thing when it came out.