What do I do here? You're in a hospital. I'm wearing a doctor's coat. I'm covered with blood. There are sharp, pointy things lying all around. Either I'm a successful killer or a fair doctor. Take your pick.
Holliday is a wizened old man wearing a doctor's coat. Born in Broken Hills in 2170, he met his wife while wandering the wastes. After she died he studied medicine in San Francisco, under the tutelage of Dr. Fung. Now, aged 70, he is Broken Hills' doctor.
Talking to Doc Holliday and listening to the story of his life will earn free healing from him (for Chosen One and the party) and also yield the fact that he knows Dr. Fung in San Francisco; allowing the Chosen One to have Dr Fung put Chip's spleen back in for free.
It is also possible to get free healing if he is asked what he does and allowed to banter a little, but it can only be done once, whereas he can be asked to talk about his life over and over again. If for some reason he is paid for healing he will charge between $50 and $300 for each person in the party.
He sells stimpaks and other items and takes only half the price if asked to trade instead of hitting the barter button.
When talked to by a low Intelligence character, he will pretend to be going to examine them, then instead steal half or their money, or $100, whichever is less. No other interaction is possible.