The Master (Fallout)

The Master is the main villain and final boss of the post-apocalyptic RPG adventure game Fallout. He is a disgusting mass of mutated flesh infused with the computer system of the underground vault where he resides. The Master is the leader of an army of "Super-Mutants" and wants to replace the (few remaining) humans of the planet with his new race of mutants, believing they will never fight amongst each other, unlike humans. A notable feature of his is that his "voice" is pieced-together from different voice samples taken from multiple people.

The Master used to be a man named Richard Grey, who fell into a vat of nuclear waste at the Mariposa Military Base, where the U.S. Government had been experimenting with the mutant F.E.V. Virus. He was in the vats for so long that he mutated into a completely inhuman blob. After a while the blob started absorbing other creatures that ventured near the base, and later merged himself with the computer systems there. As the Master grew more powerful, he started experimenting with turning his victims into separate mutant beings instead of simply absorbing them, and eventually got the idea to "unify" the wasteland with his "superior" race of Super Mutants and began sending them to conquer the human settlements of the region. Later on, the Master relocated to another vault, where he had a large cathedral built on top of and founder a fake religious group run by his human followers to lure other humans inside to be mutated by him.

The main character, the "Vault Dweller", has to destroy the Master. In addition to simply killing him, it is also possible to make the Master kill himself by convincing him that his mutants are sterile and incapable of reproducing, or by setting off a bomb found underneath the Cathedral where he is.