Dr. Spectrum is a comic book superhero in the Marvel Comics universe, and a member of the Squadron Supreme. There are actually three different incarnations of Dr. Spectrum, one of whom was a supervillain. All incarnations are essentially based on the DC Comics character Green Lantern.

Squadron Sinister

Dr. Spectrum first appeared in The Avengers #70 (November 1969) as a member of the Squadron Sinister, a group of supervillains assembled by the alien Grandmaster to fight the Avengers. The Squadron Sinister was created by Roy Thomas and was broadly based on DC Comics' Justice League. This Dr. Spectrum had a hunger to rule the earth (Defenders #13) and a power prism with it's own personality, that it lost after it had been restored by Nebulon, the Celestial Man.

A much later retcon revealed that the Doctor Spectrum of the Squadron Sinister had been created by the Grandmaster as a copy of the Squadron Supreme's Doctor Spectrum, and that the Squadron Sinister version's power prism was actually an alien Skrull in a mutated crystalline form. The Skrull-prism, named as Krimonn, was eventually destroyed.

Squadron Supreme

In Avengers #85-86 (March-April 1971), Thomas created the Squadron Supreme, a group of heroes from a parallel world who were a more direct homage of the Justice League than their Squadron Sinister predecessors. This group had its own version of Dr. Spectrum, with a human secret identity of Joe Ledger.

Dr. Spectrum used to be an astronaut, adventurer and something of a playboy. On one of his space missions he saved the life of a benevolent alien of the Skrull race. In gratitude for rescuing him, the Skrull gave Joe Ledger the Power Prism, an energy synthesizer his people had created.

Dr. Spectrum has the similar relationships to the other Squadron member as the Green Lantern character has to other members of the Justice Leage of America. His best friends are Golden Archer (based on Green Arrow) and the Whizzer (based on the Flash).

The Squadron implemented a Utopia project in the wake of their world being devastated by the Overmind. During that period the distraught former Squadron member known as Nuke died in a fight with Dr. Spectrum and his best friend, Golden Archer, was killed in a fight about the Utopia project. Both events turned Dr. Spectrum's character into a more serious one.

At last note, Dr. Spectrum and a reformed Squadron were fighting to free their world from a global dictatorship which had taken it over while the team was stranded in the main Marvel Universe.

Supreme Power

In August 2003, the Supreme Power series began to chronicle a rebooted version of the Squadron Supreme. In this version, Dr. Spectrum was an army corporal who got the nickname Doctor because of the precision he performed his secret killing missions around the world for the government. His power prism was the energy source the government took from the capsule that carried Hyperion. Joe Ledger was the only candidate who was focused and single minded enough to be able to control the prism's power and went on top secret misssions for the government. A Doctor Spectrum miniseries was launched in 2004 while Supreme Power went on hiatus. The series was written by Samm Barnes, and dealt with Joe Ledger's background, presented in flashback when the power prism was attempting to the take control of Joe's mind while he was in coma.