Doom II and Final Doom
In the Doom II final level "Icon of Sin", the boss is supposed to be a giant demon head with a fragment missing from its forehead. It says, "To win the game, you must kill me, John Romero!", distorted and in reverse to sound like a demonic chant. One can use the "noclip" cheat to enter the boss and see Romero's severed head which is skewered on a post. The player defeats the boss (without the noclip cheat) by shooting rockets into its exposed brain after activating a lift and riding it; Romero's head functions as its hit detection point; when he "dies", the boss is killed and the game is finished.
The name "Romero" is written in blood on one of the walls in level 19 "Shipping/Respawning" in Final Doom.
Read more about this topic: John Romero