Eleen was the wife of Akaar, Teer of the Ten Tribes of Capella IV, in 2267. At the time a Federation team visited, she was pregnant with Akaar's heir, with the birth imminent. When Akaar died during a coup, Maab, whose forces were victorious, assumed the title of Teer. By tradition, Eleen would be killed so that she could not bear an heir who might have a claim. James T. Kirk, unwilling to witness her execution, interrupted the murder, in the process laying hands on Eleen – an act forbidden to all but the Teer, and an act that earned Kirk a death sentence.
The Federation party and Eleen were briefly imprisoned, but Kirk and Spock managed to overpower their guards. Offered a chance at life, Eleen accepted, and fled to the nearby foothills with the Federation visitors. For several days, Capellans pursued the escapees, but Kirk and Spock confounded them with a variety of clever tactics while Dr. Leonard McCoy oversaw the birth of Akaar's son, who was named Leonard James Akaar.
At a point when McCoy was dozing, Eleen struck him with a rock, knocking him unconscious. She fled to meet with the warriors, and there claimed that she had murdered the heir and the Federation team. Maab accepted this claim, despite the fact that moments earlier, his adjutant Keel had told him that the Federation men were very much alive, and where they had dug in. The warriors prepared to leave, but the Klingon Kras demanded proof. A brief scuffle resulted, during which Kras revealed that he had stolen a phaser; he then used the weapon to coerce the Capellans. This breach of guest conduct resulted in a standoff. Ultimately, Maab granted Eleen her life, forfeiting his own in return. The manner of his death was a distraction that provided Keel with an opportunity to kill the Klingon and break the standoff. Maab's death caused the title of Teer to revert to the heir, Leonard James Akaar. Eleen served as his regent. One of her first acts as regent was signing a treaty which secured Federation mining rights to topaline on her planet. (TOS: "Friday's Child")