The Mongol conqueror is one of four figures of evil conjured by the Excalbians in The Savage Curtain to fight Kirk, Spock, Abraham Lincoln and Surak in a test of good against evil.
Genghis Khan, the thirteenth-century founder of the Mongol Empire, appears in the Original Series episode The Savage Curtain, played by Nathan Jung.
He is not the real man but an image drawn by the rock-like Excalbians from the minds of Kirk and Spock. Their spokesman Yarnek stages a contest between good and evil on the surface of Excalbia, placing Genghis Khan beside Colonel Green, Kahless and Zora of Tiburon against Kirk, Spock, Abraham Lincoln and Surak.
The Khan has no dialogue of his own and largely follows Green's lead, hurling rocks at the heroes' position and joining in the ambushes that kill the images of Surak and Lincoln. When Kirk and Spock win the final struggle he runs off with the survivors of his side.