Supergirl is the Arrowverse series where aliens let their freak flags fly. After Kryptonians like Supergirl (Melissa Benoist) and Daxamites like Mon-El (Chris Wood), the next most prominent alien race of the DC Universe of Earth-38 are the Martians, thanks to J'onn J'onzz (David Harewood). J'onn is of course the Martian Manhunter who poses as Hank Henshaw, director of the alien-fighting D.E.O. Since revealing himself to be the Martian Manhunter in season 1, J'onn has been joined by another Martian, M'gann M'orzz (Sharon Leal), as well as fought off an attack by the evil White Martians. In this week's Supergirl titled 'Far From the Tree', we learn much more about J'onn's past as well as Martian history.
Last season, M'gann left Earth and J'onn to return to Mars and help a pocket of White Martians fight a resistance against the ruling White Martians. M'gann is actually herself a White Martian, but one who has always disagreed with how the Whites tried to exterminate the Greens. She rebeled against the Whites, tried to save some Greens but for naught, and then hid on Earth for years before meeting J'onn, who is believed t be the last Green Martian. In 'Far From the Tree', M'gann summons J'onn back to Mars - with Supergirl along to help.
Upon arriving on Mars in a sweet, shape-shifting ride that would put Agent Coulson's flying car Lola on Agents of S.H.I.E.L.D. to shame, J'onn and Supergirl meet M'gann and the Resistance. J'onn is shocked to learn he isn't the last Green Martian after all. There is another, and it's J'onn's father, Myr'nn J'onzz (Carl Lumbly)! Myr'nn was freed by the Resistance after hundreds of years in White Martian captivity. The Whites wouldn't dare to terminate Myr'nn's life, as he is a holy man and prime servant of H'ronmeer, the Martian god. In DC Comics, H'ronmeer is more of a malevolent entity, the Martian god of death. The plague of fire that wiped out the Martian race is known as H'ronmeer's Curse, and was started by J'onn's evil brother Ma'alefa'ak. However, Supergirl's version of the Martian religion is decidedly more benevolent.
As the Martian creation myth that all Green Martians learn in their youth goes, Mars was once a paradise flourishing with Green Martians. H'ronmeer decided to test his sons Phobos and Diamos to be sure they were worthy to inherit paradise. He offered his children two gifts; one was a book of sacred symbols which comprise "the morals that govern Martian life" which was meant to be shared and the other was a staff - a weapon that could only be wielded by one. Phobos chose the staff, which made H'ronmeer furious. The Martian god banished Phobos to the underworld for disgracing his name and choosing a weapon of violence. Phobos and his descendants evolved to become the White Martians, who eventually clawed their way back to the surface and eradicated the Green Martians. Thus, according to the parable, the White Martians are actually an offshoot of the Green Martians, but now the J'onzz men are the only two left of the entire Green Martian race. We also learn that it's Martian custom to assume the form of your guests, which is Supergirl's clever explanation for why the Martians mostly assume human form, even though they're on Mars and should be in Green and White Martian form all the time. (This also saves considerably on the already high CGI budget.)
The staff of H'ronmeer is a psychic weapon that can harm both kinds of Martians coveted by both the White Martians and the Resistance. Myr'nn J'onzz knew its location, but it became a contest between the White Martians and the Resistance, with J'onn, Myr'nn and Supergirl on their side, to gain possession of the staff. The Resistance forces triumphed, thanks to Supergirl's help. In the end, the Resistance asked for J'onn and Supergirl to bring H'ronmeer's staff back with them to Earth and bury it. Rather than use it on their enemies, banishing the staff from their world would be a step taken by the Resistance to be better than their enemies, as the White Martians would have certainly used it on them. Supergirl and J'onn returned to Earth with Myr'nn and the staff (though the whereabouts of the staff when the trio docked J'onn's ship in his garage is a question - maybe they buried it before going back to the garage). Now the last two Green Martians in the universe make Earth their home, just like two of the last Kryptonians do.
Supergirl's version of Martian history is considerably simplified from the comics, where White Martians and Green Martians were once part of the same race but were split into two factions by the Guardians of the Universe, the ancient alien benefactors of the Green Lantern Corps. The White Martians also visited Earth in the distant path and discovered the metagene within humans, which allows certain humans to manifest super powers. There was also the Hyperclan, a group of White Martians who pretended to be superheroes and were uncovered by the Justice League. As neither the Green Lanterns nor the Justice League exist (as yet) in Supergirl's Earth-38, boiling the Martian creation myth down to a simpler parable and making the emotional crux of the story about a father reuniting with his long-lost son with Supergirl's help made the history of Mars more palatable and more powerful for Supergirl's fans.
Supergirl airs Mondays @ 8pm ET on The CW.