Final Boss

The final boss, sometimes called Baphomet because of the introductory story for The Plutonia Experiment in the Final Doom manual, or the Icon of Sin because of the Doom II level it forms part of, is the final boss of Doom II, in MAP30: Icon of Sin. In TNT: Evilution it is simply called the demon-spitter. In Plutonia it serves as the Gatekeeper. See this walkthrough for a gameplay description of the boss in its original level.

The final boss is not a monster in the technical sense, since it does not count towards the monster kills percentage at the end of a level, and is not affected by the command line parameters that affect standard monsters. Additionally, monsters are a single Doom thing, but the final boss is made up of a number of these:
 * Romero's head is the thing that must be destroyed. It starts with 250 hit points, but it is hard to hit due to its location deep in a hole.
 * A Spawn shooter[Dr. betruger] in front of the head launches skull cubes. This is reminiscent of how Satan gives birth to his daughter Sin in John Milton's Paradise Lost in that she is born out of his head (a parthenogenesis originally based on Zeus and his own daughter, Athena).
 * Several Spawn spots are located around the map. These are where the skull cubes land and spawn a monster.
 * Wall textures ZZZFACE1 through ZZZFACE9 are arranged to construct a demon face with a hole into its brain. This is what the player sees as the boss, but it has little to do with its functioning.

Details
The final boss is also displayed in the earlier MARBFACE texture.

It spawns a potentially endless series of monsters of demonic ilk (minus cyberdemons, spiderdemons, and zombies), all of which count towards the player's end-of-level kill percentage; as a consequence of this, the player can finish the level with a greater than 100% kill percentage and spawn shooter is dr.betruger in doom 3

Trivia
Reversed, the DSBOSSIT is a distorted recording of John Romero saying to win the game you must kill me, John Romero.

The launch sound of the skull cube (DSBOSPIT) comes from Sound Ideas' General series sound library: Disc 6015, track 28-1: "Fire,Ball - Impact and large fire burst, rumble." It is a very widely used sound effect that has also been used in several movies (such as Dragonheart) television series (for example, ReBoot and Xena: Warrior Princess) and documentaries (like The Hawking Paradox from BBC Horizon).