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Gilbert Gilgamesh Hamilton is a fictional character in the Known Space universe created by Larry Niven. He is one of the few science fiction detectives to appear in the genre. He is often called "Gil the Arm", both due to his affiliation with the ARM world police force, and his unusual psychic ability.
Born in Topeka, Kansas, to flatlander parents near the end of the 21st century (it is established he was born in the month of April, but 2086, 2091, 2093, and 2097 are all given as years in various stories), he emigrates to the Belt as soon as he becomes an adult. There he begins work on an arduous ten-year apprenticeship towards the acquisition of his singleship licence. During this time he works as a member of small multi-person crews.
After completing several successful trips, Gil loses his right arm. While attempting to move an asteroid with explosives, crew leader "Cubes" Forsythe miscalculates, which results in the destruction of the valuable rock. A fast moving piece of shrapnel penetrates the ship, slicing off Gil's arm and killing Forsythe instantly. The remaining crewmember, Owen Jennison, quickly seals the hull breach, stops Gil's bleeding, and manages to get him to life-saving medical facilities in time.
While recuperating from his injury, Gil broods over his future as a Belter. Their ship is missing a crew member, Gil is missing an arm, and Owen's reputation is ruined because he took (what Belters consider) unacceptable risks to get Gil back to safety.
In the low gravity of Ceres base, Gil discovers that he has a psi power. His brain, still remembering the "image" of his lost arm, can use it much as he did his own arm. He can feel and manipulate objects via ESP and telekinesis, respectively. Finding a third crewman, Homer Chandrasekhar, they make several highly profitable trips over the following year. Gil finds his "imaginary arm", though not strong, to be an asset, as he can reach through walls, and accomplish tasks beyond the ability of a normal person. After six months, Gil has earned enough to repay all his medical fees, with a comfortable cash reserve left over.
Despite much disapproval from Owen and Homer, Gil decides to return to Earth and seek to get his citizenship back. On Earth, he can easily get a transplant to replace his missing arm. In the Belt he would have to pay exorbitantly high fees for a transplant, or settle for a prosthetic. Gil, by a quirk of his own nature, can not live with a prosthetic.
Gil receives his new arm, but finds he can still dissociate his imaginary arm from his real one, and reach through walls, flesh, and even vidphone screens to manipulate objects he sees in them. Shortly afterward, Gil finds out that his new arm had not come from a condemned criminal as he had hoped, but from the captured stock of "organleggers", black market dealers in illicit organ transplants.
To make amends, Gil joins the ARM, the elite global police force.
As an ARM, Hamilton is a high-tech detective, who hunts organleggers and other criminals for a living. With his unusual psi power, he is formidable and highly feared among his enemies.
- Death by Ecstasy (1968)
- The Defenseless Dead (1973)
- ARM (1975) 
- Plot: Hamilton is called to the scene of a murder. The victim is Dr. Raymond Sinclair, a brilliant scientist who has invented a mysterious device that creates a bubble of accelerated time. The murder scene is a locked apartment at the top of a high-rise, where the prime suspect is a beautiful young woman whom Gil refuses to believe is the killer.
- The Patchwork Girl (1980)
- The Woman in Del Rey Crater (1995)
The Long Arm of Gil Hamilton (1976) (ISBN 0-345-30050-5) contained the first three stories
The Patchwork Girl (1986) was published alone as a novel (ISBN 0-441-65315-4)