Doctor Spectrum was a member of the Squadron Supreme.
Doctor Spectrum was an alien superhero from a distant world where they he was a member team of heroes similar to the Avengers called the Squadron Supreme. The people of their world feared their power and turned against them. As a final solution, Hyperion destroys his home planet along with his team on it, escaping into space in his Citadel.
Using the Reality Gem, Doctor Spectrum alters reality so the Avengers are all criminals with darker costumes and the Avengers Tower is headquarters of the Squadron. Due to a spike in energy, Iron Man sees the real reality and manages to convince his team to come together. However, Spectrum has created a machine that will give him complete control over reality, and plans to alter history so the Avengers were never born. Captain is able to get a hold of the stone and revert reality back to normal. The Squadron leaves with Nighthawk activating charges placed at the base of Avengers Tower. The Avengers manage to prevent the structure from falling onto New York in time for J.A.R.V.I.S. to activate the repair systems.
In "Spectrums," it is revealed that Nighthawk and Hyperion attached the Power Prism to Doctor Spectrum in order to destroy the Squadron Supreme's planet. Ant-Man led Captain America, Iron Man, and Thor to Doctor Spectrum's hideout where it turned out that he was one of the people that was sold Ant-Man's technology. The technology in question had allowed Doctor Spectrum to get control of the Power Prism. During the fight, he harvested the feelings of Captain America, Iron Man, and Thor in order to create copies of Winter Soldier, Ultron, and Loki. After Ant-Man managed to free Doctor Spectrum from the Power Prism with information that was learned from Falcon, Doctor Spectrum reverted back to Billy Roberts. In the aftermath of the fight, Iron Man and Ant-Man hooked Billy Roberts up with S.H.I.E.L.D.'s space program to help in it's space exploration and to find a suitable planet for Billy to reside on. As for the Power Prism, it made it's way back to Nighthawk where it no longer needs a host and forms it's own body modeled after Doctor Spectrum.
In the episode "Avengers' Last Stand," the Power Prism's Doctor Spectrum form joins the Squadron Supreme into enacting Nighthawk's plot against the Avengers. In the episode "Avengers Underground," the Power Prism's Doctor Spectrum form is defeated by Ant-Man as Captain America uses the Power Prism to turn the sun blue so that Black Widow can defeat Hyperion.
As the Squadron Supreme is based off of DC's Justice League, Doctor Spectrum is the SS version of Green Lantern. His voice actor, Phil LaMarr, previously voiced the John Stewart Green Lantern in the Justice League cartoon.