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  1. Games
  2. RPGs
  3. Fallout

D&D's most annoying rule helped Fallout co-creator Tim Cain get his big break at legendary RPG studio Interplay after he flexed on the job interview

News
By Ali Jones
Published 10 March 2026

THAC0 comes for us all

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Fallout 1 power armor helmet
(Image credit: Interplay)
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Fallout co-creator Tim Cain owes the job that truly got him started as a game developer to his ability to flex his knowledge of one of D&D's most annoying rules in his job interview.

In a new YouTube video asking whether his success as an RPG developer was down to good fortune or good planning, Cain explains how he found himself at Interplay, the legendary studio that created Planescape: Torment, Icewind Dale, and Fallout, and published Baldur's Gate, to boot. Having spent countless hours playing tabletop games and teaching himself to code throughout high school, Cain ended up at University of California Irvine, where he says he was "surrounded by game companies."

"In the evening I'd often play tabletop RPGs with grad school friends of mine," Cain says, "because we didn't have any money so we couldn't go do anything. We were kind of stuck in the student housing there, so we played a lot of games." Many of those were based around GURPS (Generic Universal Role-Playing System), which would go on to inform much of Cain's work, and was the original choice for Fallout's game system.

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Eventually, Cain decided to leave graduate school, and sent his resume to Interplay, which was only about ten miles away from his house. He was hired as a contractor, and the rest is history - except it might not have been, but for something that happened during the job interview.

"They asked me if I knew THAC0," Cain says, referring to a now mostly-defunct system for determining if a D&D attack hit its target. THAC0, which stands for 'To Hit Armor Class Zero', is best summarized as the reverse of D&D's current armor system - the lower your Armor Class, the better, and you're trying to roll above your character's THAC0 stat minus your target's AC. Primarily associated with the 2E era, when Cain was playing his tabletop games, it was removed from 3E and is now infamous for its complexity compared to the modern system.

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In his interview, Cain was up against one other programmer, and "we were both about equal in coding skill." But when Interplay asked the pair if they knew what THAC0 meant, Cain says he couldn't just answer that question, but "asked them if they wanted the values for THAC0 for each of the four major D&D classes at level one." They said yes, he reeled off the numbers, and he got the job.

The rest is history - though Cain has done a very good job of documenting that history via his YouTube channel, right down to the time he had to throw a fake pizza party to sell his fellow devs on the idea for Fallout. The moral of the story, however, is not just that having somewhat obscure knowledge can help you get a job - throughout the video, Cain makes it clear that the choices he made throughout his life put him in the best possible position to have the chance to make an RPG when the opportunity arose. His coding experience, his part-time job, and the many, many hours he spent learning TTRPG systems inside and out all helped him on the journey to the Wasteland.

Fallout co-creator "would have gone in a different direction" than Bethesda did with the RPG series, but "sales say people love what they did"

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Ali Jones
Ali Jones
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Managing Editor, News

I'm GamesRadar's Managing Editor for news, shaping the news strategy across the team. I started my journalistic career while getting my degree in English Literature at the University of Warwick, where I also worked as Games Editor on the student newspaper, The Boar. Since then, I've run the news sections at PCGamesN and Kotaku UK, and also regularly contributed to PC Gamer. As you might be able to tell, PC is my platform of choice, so you can regularly find me playing League of Legends or Steam's latest indie hit.

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