At the end of last week's Supergirl, J'onn J'onzz made a trip to the alien friendly bar that Maggie Sawyer showed to Alex Danvers. While there, he discovered that he isn't the last Martian… M'gann M'orzz worked as the bartender. We'll be seeing more of her tonight, so now seems like a good time for a primer on Miss Martian.
As comic book characters go, she isn't that old. She first appeared in Teen Titans Vol 3 #37 back in August of 2006, created by Geoff Johns and Tony Daniel. M'gann was sent in a ship to the Vega system when she was young while the civil war between the White and Green Martians took place. It's unknown how she made the trip back to Earth, but she ended up joining the Teen Titans and had a bit of a rocky start. She was on the team until a misunderstanding with Ravager… involving a pie to the face… made her leave the team.
The Titans would later come across her again in Australia while trying to find Raven. Miss Martian discovers that one of the new team members, Bombshell, was actually a traitor. But before she could out him, he used an incendiary device to reveal that M'gann is actually a White Martian, not a Green Martian like J'onn J'onzz. She helped the team stop Bombshell and was once again made a Teen Titan by Cyborg.
From there, M'gann has had a rough go. She learned of a future where all Martians are slaves and that she was the personal slave of Sun Girl from Titans East. She then got caught up with the Amazons attacking Washington DC which lead to her having to fight Supergirl and later Artemis, then having to save Wonder Girl's mother Helena. She then met her future counterpart that called herself Martian Manhunter. After a long battle, trace elements of her future-self's personality merged with M'gann's own. This lead to an almost split personality and her leaving the Titans. She would spend a great deal of time posing as a new Star-Spangled Kid to infiltrate the Dark Side Club, an underground fight club for brainwashed young heroes run by the Clock King and the Terror Titans.
Even though she is a White Martian, she possess the same basic powers as J'onn J'onzz… which is a lot from telepathy, telekinesis, regeneration, shape-shifting, super strength, super-speed and a boat load of different vision abilities… though we haven't seen all of these on the TV series, so that may be limited. She brings an interesting dynamic to the television series, putting the whole White / Green civil war front and center… assuming they go with her being a White Martian posing as a Green. Guess we'll find out soon.