The Talosians were a quite intelligent sentient species from Talos IV. They were a technologically advanced culture but a nuclear holocaust left their planet virtually uninhabitable. The leader of the Talosians was called the Keeper.
The survivors lived underground and became dependent on their mental ability to create real illusions. Their dependence upon these illusions for mental stimuli cause them to begin capturing other species to use for their illusions.
Those that did survive, were incapable of reclaiming their planet’s surface. They decided to breed slaves to do this for them.
The SS Columbia crashed on Talos IV in 2236. All aboard were killed but one female, Vina. They repaired her injuries but left her disfigured.
First contact with the Talosians took place in 2354 when Captain Christopher Pike of the U.S.S. Enterprise made contact with them. Pike led an away team to the surface. The ship had received a distress signal from the S.S. Columbia. The ship was lost 18 years earlier.
They tried to make Pike and a Columbia survivor, Vina, the parents of the slaves. The Talosians realized that humans would be unsuitable parents for the slaves. It was their will of freedom that the Talosians came to the conclusion.
Captain Pike ordered a General Order 7 for Talos IV. This prevented contact with the Talosians. By 2267, this was the only death penalty offense the Federation still had.