Marta was an Orion inmate at the Federation asylum on Elba II. She was delusional, and seductive. Marta served as somewhat of a consort to Garth of Izar during his attempted take-over of the colony in 2268.
After James T. Kirk was captured by Garth, he placed him and Marta alone in a room where she tried to seduce him. She was unsuccessful and tried to stab Kirk, who managed to fight her off. Marta died on the planet's toxic surface when Garth used her as an example of what would happen to the hostages if he was not allowed to leave the colony. He showed her mercy by blowing her up while demonstrating a new explosive, instead of letting her choke to death. (TOS: "Whom Gods Destroy")