Martian Manhunter

The last known green Martian, J'onn lives on Earth and is a founding member of the Justice League

Gotham City
After being transplanted to Earth from his home planet Mars by the scientist Dr. Erdel, J'onn J'onzz quickly took up the mantle of a deceased detective named John Jones in Gotham City. He formed a crimefighting duo with fellow superhero Starman. Despite being on the same side of the law, the duo constantly found itself at odds with the already established team of Batman, Nightwing, and Robin. J'onn and Starman would ultimately leave Gotham and set up a base on the Moon.

Eclipso
While living on the Moon, Starman and J'onn encountered three aliens claiming to be servants of Eclipso who were digging for what turned out to be a black diamond. J'onn and Starman held their own against the minions of Eclipso, but then Starman was cut with the black diamond and subsequently possessed by Eclipso. J'onn proved to be no match for the powerful Eclipso by himself, so he phased into the Moon to escape capture. Eclipso would later be defeated by Superman and Captain Marvel in the Sahara Desert after Captain Marvel's Shazam! lightning bolt forced Eclipso to change back into Starman.

Justice League
J'onn was abducted along with several other superpowered beings living in the Earth's solar system (including Wonder Woman, Superman, the Flash, and Black Adam) by the tyrant Mongul to participate in his gladiator games on War World. The team was able to escape from the planet after helping the resistance defeat Mongul's army, and upon returning to Earth formed the Justice League. J'onn was influential in getting his good friend Starman membership onto the team.

During the events surrounding Owlman's attempt to destroy Earth-One, J'onn was almost killed by Jemm, the Saturnian member of the Crime Syndacite, after he was able to infiltrate the Hall of Justice disguised as the Red Tornado. Jemm through J'onn onto burning computer equipment and left him to die in the burning down Justice League headquarters. J'onn was able to barely escape and ended up fighting Jemm again during the huge battle between teh Justice League and the Crime Syndacite. J'onn proved to be a very minor member of the League, usually only appearing whenever his mental powers were needed.

Shortly after the appearance of Superboy-Prime, J'onn felt himself being called to return to his home planet of Mars. He quickly did, and upon arriving he found the planet to be a desolate wasteland far from what it was like when he lived there. In his head he heard the voices of numerous Martian ghosts, begging him to free them. One particular voice he recognized as his younger brother's, T'omm J'onzz. J'onn was then approached by the Martian god H'ronmeer, who told him that he needed to sacrifice himself so that the Martian race could thrive again. H'ronmeer revealed to J'onn that the Martians had died out thousands of years ago due to a psychological disease that would make the any Martian who had it perceive themselves to be burning alive mentally and physically until their body would shutdown and die. The Martian ghosts then revealed to J'onn that it was H'ronmeer who had inflicted the horrible epedimic on the Martian race because they turned away from him and became a secular society. J'onn was left utterly perplexed and opted to let H'ronmeer have his way H'ronmeer intended to deconstruct J'onn down to the molecular level, then reconstitute each molecule into a new Martian being, combining the physical matter with one of the Martian ghosts. Sensing danger, Superman (now in his blue form) teleported to Mars to help J'onn. Superman was barely able to convince J'onn to not allow H'ronmeer to execute his plan, but not before he was able to begin the process (resulting in some of J'onn's matter to be fused with another Martian who has yet to resurface). J'onn and Superman were able to defeat H'ronmeer, and actually ended up killing him.

Personality
Martian Manhunter is usually very quiet and reserved. He rarely voices his opinion during Justice League meetings, being content it would seem with whatever the majority of his fellow members want. He may have been psychologically scarred by several events, including: Nevertheless, J'onn is admired by all of his teammates as being loyal and reliable.
 * Being suddenly ripped away from his home and loved ones on Mars and being forced to live in a strange land
 * The "death" of his closest (and for a long time only) human friend Jack Knight (Starman) during the events of Eclipso's resurrection of Golden Pharaoh
 * His realization upon being called to Mars by the Martian god H'ronmeer that all of his fellow Martians are dead, and have been for thousands of years because Dr. Erdel's device transported him across both space and time

Quotations

 * 1) Martian Manhunter: "..."
 * 2) Martian Manhunter: "Mhm."