Dog and God

Dog is a schizophrenic captured Nightkin assisting the Father Elijah in breaching the Sierra Madre Casino in the add-on Dead Money. His alternate personality, God (referred to by the former as simply "the voice"), is trying to break Dog free of Elijah's grasp.

The "Dog" personality is activated by the sound of Father Elijah's voice, and the "God" personality is activated by the sound of his own voice (via holotape or radio). When one personality is dominant, the other is said to be in "the cage".

Background
It's not clear which personality was the "original" and which was the one that appeared after schizophrenia developed.

Hand-picked by the Master to serve in his Nightkin army, Dog was crushed by the Master's defeat. He eventually found Sierra Madre, where Elijah took advantage of his need for a "master" figure to enslave him, using him as a tool for capturing potential treasure-hunters and later for activating the Sierra Madre Gala. Dog is extremely loyal and will follow the commands issued by his master's voice to the letter, even when it puts him in danger. He also appears to suffer from some sort of eating disorder, as he will eat anything, even Ghost People when he his hungry. This eventually led to him accidentally eating an explosive collar off a dead treasure hunter, putting him in the same situation as the many victims he had dragged to the Sierra Madre. He hates "the voice", and is willing to do anything to be rid of it, going even to the point of self-harm. Pain hurts him, but also quietens the voice, so he will go to extremes such as scarring his body and putting his hand in bear traps in order to make it stop.

God is very different to Dog. He is quiet, articulate, and far less pliable than his counterpart. He claims that he only wishes to help Dog, and the best way to do that is to eliminate Elijah. He does not care for the treasure of the Sierra Madre, and frequently comments on the Courier's perceived greed. He is, however, less adept in combat than Dog, as he is far less used to the Nightkin body and lacks the bloodlust of his other personality.

Appearances
Dog and God appear in Dead Money.