TOS Season 3 Episode 22 The Savage Curtain

Plot

The Federation starship Enterprise arrives at the volcanic planet of Excalbia to conduct a geological survey. Impossibly, sensors detect carbon-based life on the planet's surface. The image of Abraham Lincoln drifts toward the ship on the viewscreen. Though skeptical that the figure is the real president, Kirk extends full presidential honors as he transports aboard the ship. Lincoln is human, has no knowledge of technology past the 19th century, but is somehow familiar with the Vulcan philosophy of Nom (meaning "all"). Lincoln invites Kirk and Spock to accompany him down to the planet where an area has appeared with Earth-like conditions. Despite the possibility that the livable conditions are an illusion, Kirk accepts, reasoning that the Enterprise's mission demands they accept any offer of contact with new life.
Once on the planet, Kirk and Spock discover their tricorder and phasers did not transport with them. They are met by Surak, "the father of Vulcan civilization", who died centuries before. A rock-like being with clawed hands and glowing eyes atop a bulbous head, named Yarnek, announces that the inhabitants of the planet wish to conduct an experiment to determine which human philosophy is stronger: good or evil. In this experiment, Earth warlord Colonel Phillip Green, Klingon warlord Kahless, a practitioner of unethical experiments on humanoids named Zora, and Genghis Khan, together representing evil, will be pitted against Kirk, Spock, Lincoln, and Surak (representing good) in a fight to the death.
Colonel Green offers Kirk an alliance against the Excalbians so that they can all safely return to where they came from, but this is only a distraction for a surprise attack. Kirk and his companions fend off their opponents and run for cover. Kirk and his companions remain resolved that the Excalbians are the true enemy. Kirk attacks Yarnek, but the alien's body is too hot to touch. To force them to fight, Yarnek breaks down the shielding between the matter and anti-matter on the Enterprise, ensuring the ship will explode unless Kirk's force emerges victorious in four hours.
Kirk and the others begin to manufacture spears. Surak, whose life experiences have taught him that persistent efforts at peace are the best course, obtains permission to go alone to the enemy camp and negotiate. Green's group kills Surak and lures the others in by mimicking Surak crying for help. Lincoln offers to sneak around and free Surak while Kirk and Spock provide a diversion. When Lincoln arrives, he finds Surak's corpse and the waiting Kahless and Green, who kill him.
Though now outnumbered two-to-one, when Kirk and Spock confront Green's group in battle, they quickly flee. Despite the conditions of a fight to the death remaining unfulfilled, Yarnek announces that the experiment is over. He concludes that there is nothing different between good and evil because the methods used to fight each other are the same. Kirk explains that the similar methods of how the two fight each other does not define them as the same. What defines them is the things for which each of them fight. The Excalbians allow Kirk and Spock to return to the Enterprise. Though the mystery of Lincoln and Surak remains unsolved, Spock offers the conjecture that the Excalbians, using their apparent ability to transform matter, transformed other living beings into the likenesses of Lincoln and Surak, then tapped Kirk and Spock's minds to create the personalities which they imagined those historical figures had.