Marla McGivers Singh is the secondary antagonist of the Star Trek episode "Space Seed".
She was portrayed by the late Madlyn Rhue.
In the 2260s, McGivers had joined Starfleet. A historian by trade, McGivers was drawn to strongmen throughout history, including Alexander the Great, Napoléon, Richard the Lionheart, Leif Ericson, Flavius, and 20th century Augment tyrant Khan Noonien Singh.
She was assigned to the USS Enterprise in 2267 as the ship's historian. McGivers was friends with several members of the crew, including Pavel Chekov. She was one day called to be on a landing party to explore the ancient derelict SS Botany Bay. Exploring the ship, they found Khan in cryostasis. With his tube malfunctioning, Khan was revived by Kirk and the Enterprise crew.
Using her fascination with him as a way to manipulate her, Khan was able to get McGivers to turn against the Enterprise crew. After he escaped from his quarters on the Enterprise, McGivers beamed Khan to his ship, where he revived the rest of his surviving crewmembers. Khan's people reboarded the Enterprise and swiftly took control of the Federation starship.
Seeing Kirk being slowly tortured to death in the ship's decompression chamber by Khan, McGivers had a change of heart, and freed Kirk from the decompression chamber. After defeating Khan in combat, Kirk and his crew regained control of the Enterprise. McGivers, Khan, and the other Augments were all placed under arrest.
At the hearing that followed, Khan and his people were sentenced to exile on Ceti Alpha V. Kirk gave McGivers a choice, either go with Khan or face a court martial. As Khan and McGivers were now in love with each other, she decided to accompany Khan into exile.
After the Enterprise left Khan, McGivers, and the Augments on Ceti Alpha V, McGivers married Khan. They began to forge a new life on Ceti Alpha V. At first things seemed to be going well, but six months afterwards Ceti Alpha VI exploded, laying waste to Ceti Alpha V. McGivers was infected by a Ceti Eel by one of Khan's rivals. The eel was one of the few creatures to survive the devastation of the planet. Ordered to kill Khan, she committed suicide instead.
Khan blamed Kirk for McGivers's death, and it was one of his primary motivations in taking revenge upon Kirk when he and his followers escaped Ceti Alpha V on the USS Reliant.
A couple years after the Battle of the Mutara Nebula, Kirk, McCoy, Spock, and Sulu returned to Ceti Alpha V to learn more about Khan's time in exile. Discovering the tomb where McGivers had been laid to rest, Kirk had McGivers exhumed and then cremated. He beamed her ashes into the debris field created by the explosion of the Genesis Planet, leaving her and Khan together again and hopefully at peace.
McGivers was initially slated to return for The Wrath of Khan. However, by then, Madlyn Rhue was suffering from multiple sclerosis and the disease prevented her from being able to return. As director Nicholas Meyers did not want to recast the part, the McGivers character did not return, and was instead written as being deceased by 2285.