Class-M planet, home of the Talosians. Thousands of centuries ago, a nuclear war nearly wiped out the entire civilization; the survivors lived underground where they became dependent on illusion-creating technology.
The S.S. Columbia crashed here in 2236; the U.S.S. Enterprise visited in 2254. As of 2266, contact with Talos IV was forbidden by Starfleet, due to the addictive qualities of the illusion technology. Captain Christopher Pike, however, returned to the planet so he could live out his days unencumbered by his physically damaged body.