"The Savage Curtain" is a third season (and the antepenultimate) episode of the original science fiction television series, Star Trek, first broadcast on March 7, 1969, and repeated July 1, 1969. It is episode #77, production #77, written by Gene Roddenberry and Arthur Heinemann, based on an original story by Gene Roddenberry, and directed by Herschel Daugherty.
In this episode, aliens force Captain Kirk and First Officer Spock to join forces with "Abraham Lincoln" and "Surak" to battle villains in a contest between good and evil.
The Federation starship Enterprise arrives at the volcanic planet of Excalbia to conduct a geological survey. Sensors curiously pick up the presence of carbon-based life on the surface which Science Officer Spock deems impossible owing to Excalbia's extreme volcanism. Suddenly, the image of a seated Abraham Lincoln appears drifting toward the ship on the viewscreen. While Spock is skeptical that the figure cannot possibly be the real president, Kirk extends full presidential honors to the former leader of the United States as he transports aboard the ship. The president appears to be human, claiming to be "all too human". Lincoln 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, as a patch of "Earthlike" condition appears on the planet. Kirk accepts despite objections from Chief Medical Officer Dr. McCoy and Chief Engineer Scott. Lincoln reassures them that they will be perfectly safe.
Once on the planet, Kirk and Spock discover their tricorder and phasers did not transport with them. They are met by a Vulcan named Surak, "the father of Vulcan civilization". Spock does not believe this Surak is real and accordingly refers to him as the "Image of Surak". Nearby, a boulder changes form into a rocklike being with clawed hands and several glowing eyes atop a bulbous head. The alien, named Yarnek, announces that the inhabitants of the planet wish to conduct an experiment to determine which opposing human philosophy is stronger — good or evil. The inhabitants of the planet, as well as the crew of the Enterprise, will be able to witness the drama but will not be allowed to interfere. The test will be a simple one of survival. Kirk grabs the alien but withdraws in pain, as the alien is as hot as lava.
The alien introduces four more beings: Earth warlord Colonel Green, who led a genocidal war during the 21st century); Klingon Kahless, founder of the Klingon Empire; a feral-looking woman named Zora (who conducted brutal experiments on the primitive tribes of Tiburon); and Earth barbarian Genghis Khan. The alien pits Kirk, Spock, Lincoln, and Surak against Green, Kahless, Zora, and Genghis in a fight to the death.
Colonel Green, notorious for attacking his enemies while in the midst of negotiations, starts the battle by offering Kirk a truce, stating that they should not fight for the amusement of the Excalbians. Meanwhile, Green's associates secretly ready an attack. Familiar with Green's treachery, Kirk and his companions are prepared for the surprise attack. They manage to fend off their opponents and make a run for cover.
Kirk protests the experiment and refuses to continue the battle. The Excalbians offer an incentive to fight by threatening to destroy the Enterprise in four hours if Kirk does not comply. Without another choice, Kirk and the others plan strategies and begin to manufacture spears. After another round of rock tossing and spear throwing, Surak surmises that their belief in peace is being tested, and offers to negotiate with their enemies. While Spock says he will fight alongside Kirk, he urges Kirk to let Surak try.
Surak makes his way to the enemy camp to talk while Kirk and Lincoln continue planning their strategy. A moment later, a scream of pain is heard in the distance followed by Surak shouting for Spock's help. Green tries to lure Kirk from hiding by taunting him about Surak's need for assistance. Spock believes it is a trick, saying a Vulcan would not cry out so. Lincoln offers to sneak around and free Surak while Kirk and Spock cover him. When Lincoln arrives, he finds Surak dead and discovers Kahless's uncanny ability to mimic voices.
Kirk impatiently waits for Lincoln to return and runs toward him when he finally appears. Lincoln shouts a warning not to come any closer and that the enemy is planning a trap. Lincoln then collapses dead with a spear in his back. Angered, Kirk vows to finish the battle and engages the enemy head on. Kirk and Spock easily defeat them one at a time and when Green is killed, the others panic and flee for their lives.
With the fight over, the Excalbian reappears and announces that while evil retreats when confronted with force, there is no great difference otherwise between the two philosophies. At this point Kirk states that the representatives of evil were motivated by a desire for power, but the good were moved to protect the Enterprise crew, implying it is not the methods but the ends that distinguish good and evil. The aliens conclude their experiment and allow Kirk and Spock to return to the Enterprise.
The costume created for Colonel Phillip Green was thought to have been recycled later as Mork's (Robin Williams) red spacesuit (but with the white triangle) on both Happy Days and Mork & Mindy.