Excalbian scientist who conducted experiments on members of the U.S.S. Enterprise crew without their consent. Yarnek (who appeared to the Starfleet crew to be a creature composed of rock and stone) lured the Enterprise to the planet in 2269 by sending a replica of human historical figure Abraham Lincoln aboard the ship.

Enterprise Captain James T. Kirk and his first officer Spock were included in a contest of "good versus evil," allying them with Abraham Lincoln and Vulcan historical figure Surak against Klingon historical figure Kahless, human historical figures Ghengis Khan and Colonel Green, and the insidious scientist Zora. When "good" defeated "evil," Yarnek released the Enterprise officers, yet stated he would be continuing his experiments.