Harry Collins was a citizen of Nipton until the Nipton Massacre in 2281.
Harry Collins was highly paranoid, and, as a result, suspicious of the other citizens in Nipton, being convinced that several of them, including Mayor Joseph B. Steyn, was conspiring against him, and trying to find and steal his "vital essence". As a result, he barricaded his house, put a lock on almost everything openable in it, and littered it with traps.
He was presumably killed when Caesar's Legion attacked Nipton, but at least one legionary seems to have fallen victim to his traps.
Harry Collins is mentioned only in Fallout: New Vegas.