This article originally appeared on Den of Geek UK.

Somewhere in Moscow in 1984, 29-year-old computer engineer Alexey Pajitnov sat at his work station, deep within a building called the Soviet Academy of Sciences. Here, in front of his hulking computer, an Elektronika 60, Pajitnov was working on one of his latest programs. If you’d been one of his superiors, Pajitnov would have told you that he was examining its code for bugs. But in reality, he was addicted.

Had you taken a look over Pajitnov’s shoulder at what he was working on back then, it’s likely you wouldn’t have thought much of it in any case. Just a few characters juddering down a screen – the Elektronika being such a crude computer that it could only display text. But what the young programmer had in front of him was the early prototype for what he’d later call Tetris – a single word cobbled together from tetromino and tennis – a game which would soon sweep the entire world. It was simple, absorbing, and above all, utterly addictive.

“The program wasn’t complicated,” Pajitnov told The Guardian in 2009. “There was no scoring, no levels. But I started playing and I couldn’t stop. That was it.”