Dog and God

Dog is a psychologically disordered (multiple personalities) Nightkin assisting Father Elijah in finding people to breach the Sierra Madre Casino in the Fallout: New Vegas 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
Though it is not made explicitly clear, dialogue with both the "God" and "Dog" personalities suggests that God is the re-emergence of whatever remains of the mind of the original human before (s)he was mutated by the FEV virus while Dog is the mind created to serve in the Master's army.

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 is 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. Like most Nightkin Dog exhibits true multiple personality disorder. He hates "God" or "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 quiets the voice, so he will go to extremes such as scarring his body and putting his arm in a bear trap in order to make it stop.

God is very different from Dog. He is quiet, articulate, and far less pliable and more sinister 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. Also when you are eavesdropping on him through the radio you can hear him saying "I wonder if I can tear off the Pip-boy on his arm without killing him...hmmm..."

Endings

 * If Dog forgets himself, so does the voice that raged within him. After their passing, a new voice speaks within the mutant's shell. It is difficult for the voice to remember the two it once was... there was the beast, Dog consumed by hunger... and the other in reverse... the one consumed by control. Both were driven by need for the other. The Courier brought them together, somehow, joined the two into one. All that happened at the Sierra Madre, is a faint memory to the new personality... like a flickering light in the clouds of the mind. The new voice does not think of the Courier again until the battle at the Divide reaches his ears. The battle between the two couriers, beneath the torn skies and the Old World flag... each bearing a message for the other. And the mutant prays that the Courier that had saved him... had been saved in return.
 * If Dog falls in the Sierra Madre casino, two die as one. Dog dies hungry, alone, frightened. The voice in his head dies with him. Screaming. Furious. Enraged. But the voice is gone, and Dog is grateful. At least Dog is dead and the voice needs to watch over him no more. In the moment before their lives end, the wall between the two personalities falls. The two become silent as they see the chain between them. Hunger and control are twin greeds, something Dog and his shadow had never realized.
 * If Dog is convinced to obey the voice, God thanks the Courier and promises to one day release Dog. He then goes into the wasteland in search of 'others like him' and tells them of the Courier.
 * The Courier can tell Dog to tear apart God in his mind, making him see the player as Master.

Notable quotes

 * "No, you wouldn't. If you did, you won't escape this place alive. I'd shatter every one of your limbs to splinters and leave you here. "
 * "I'll prop your broken body in view of the Sierra Madre so you can see what you came to steal... forever out of reach as you die."
 * ''"Where is Master? Did he go away? Dog will be good this time."

Appearances
appears in the Fallout: New Vegas add-on, Dead Money.