TAS Season 1 Episode 7 The Infinite Vulcan

Plot

While exploring the newly discovered planet Phylos for possible Federation colonization, Lt. Sulu picks up a walking plant, called a Retlaw, and is poisoned by a stinger. The plantlike alien beings who inhabit the planet approach the Enterprise landing party and their leader, Agmar, saves Sulu's life. The Phylosians say they were nearly wiped out by a mild terrestrial disease that was brought to the planet by Dr. Stavos Keniclius, a Terran scientist who survived Earth's Eugenics Wars.
A giant clone of Keniclius, named Keniclius Five, kidnaps First Officer Spock. Keniclius has survived through the centuries by periodically transferring his consciousness into a new, more advanced clone body. He believes the galaxy is as war-ravaged as Earth was when he left it. He plans to enforce peace on the galaxy with the aid of a fleet of Phylosian ships and a giant clone of Spock that he's created by transferring Spock's consciousness into it, leaving Spock's original body a mindless shell. The newly awakened Spock Two uses his Vulcan telepathic abilities to mind meld with his original self and save his life. The two Spocks, in concert with Captain James T. Kirk, convince Keniclius that the need for his plan no longer exists. Spock Two and Keniclius Five devote themselves to restoring the Phylosian civilization as Spock One departs with his shipmates.