18 Mind-Blowing Facts You Never Knew About DOOM

14. Romero's Payback

John Romero eventually found his own severed head in the game, and instead of bringing attention to the in-game prank or outright erasing it, he decided to one up them with a jest of his own.

Upon entering the Icon of Sin’s domain, you'll hear an eerie voice speak demonic sounding gibberish. This is actually Romero himself stating, “To win the game, you must kill me, John Romero!" Romero had gone to sound designer Bobby Prince and recorded this line, reversed it, and snuck in into the level.

Romero hoped that this would remain secret until the release of Doom II, in which its discovery would act as a sort of comeuppance to their prank. Instead, it was discovered the very next day.