James T. Kirk/Relationships/Enemies/Khan Noonien Singh

One of the most violent rivalries of his life was the bitter feud between himself and 20th century Augment dictator Khan Noonien Singh.
In 2267, the Enterprise discovered Singh and his followers aboard the and awakened them. Unaware of Khan's true identity, Khan took advantage of Kirk's hospitality to familiarize himself with the ship and its systems. After identifying Khan, Kirk had him restricted to quarters, prompting Khan to implement his plan to seize control of the Enterprise.
With the help of Lieutenant Marla McGivers, Khan assumed control of the Enterprise. The augments were eventually subdued with anesthetic gas, causing Kirk and Khan to engage in hand-to-hand combat. Realizing he was no match for Khan's augment strength, Kirk subdued him with a heavy flow-control rod. After defeating Khan and his followers, Kirk exiled them to the then habitable world of Ceti Alpha V. ()
Khan later sought revenge against Kirk after McGivers had died in exile. By that time, Ceti Alpha V had lost its ability to support much of the life it had once sustained. To exact his revenge, Khan hijacked the USS Reliant and stole the Genesis terraformation torpedo, whose research and development team included Kirk's old flame Carol Marcus and his bitter, resentful son by Carol, David Marcus. The torpedo's detonation aboard the Reliant, while it was inside the Mutara Nebula, killed Khan and those who were left of his people. But the Enterprise, and Kirk, barely managed to escape the torpedo's blast radius. ()