Star Trek: 10 MORE Alien Encounters Before First Contact

The Platonians were encountered by the crew of the Enterprise in the 23rd Century. They were a then-modern-day reproduction of Ancient Greece, having modeled their society on the teachings of Socrates and Plato.

The group were natives of the planet Sandhar, having been selected and bred via a form of advanced eugenics. Leaving their planet, they settled on Earth, studying the aforementioned philosophers, while the sun of their homeworld went supernova.

When the Ancient Greek civilization died out, they left Earth, traveling until they settled on the world that would later host Kirk and the landing party. Here, they encountered the drug kironide. This substance granted them long life, telekinetic powers, and telepathy. They became the very gods that had ruled over Greece, growing decadent and old. 

Much of their knowledge was lost. Having no need for medicine, their leader Parmen was almost struck with a fatal wound on his leg. He was saved by Dr. McCoy, though the events of that away mission ended up having long-lasting effects on the Platonians, the crew of the Enterprise, and TV censors for years to come.