He is a doctor for the Boomers at Nellis Air Force Base and can usually be found inside the Nellis medical station. He usually treats small ailments such as bug bites, but also treats more life-threatening conditions.
Volare!: The Courier can help Argyll by healing his patients, a Medicine skill of 60 is needed to heal all of them, but a Medicine skill of 40 or Speech skill of 35 can be used to convince him to let you take a look at them. You can't try to treat them without his go ahead.