In "The Savage Curtain," an Excalbian (or several) forces Kirk and Spock to participate in a "good vs. evil" war. In addition to the two Starfleet officers, the "good" side consists of Abraham Lincoln and Surak; the "evil" side is represented by Kahless, Zora, Genghis Khan, and Colonel Green.
Where did these humanoids come from? Did the Excalbians cause the Enterprise crew to hallucinate? Did the Excalbians literally create life? Were they facsimiles of the individuals, like the Douwd's copy of his wife?