Tau Beta IV was a planet in a remote part of the Federation, somewhere in the galaxy's Alpha or Beta Quadrants, the fourth planet in the Tau Beta star system. By the 23rd century, Tau Beta IV had only been recently surveyed by a development team for colonization.
Study and analysis of the planet showed it to be rich in dilithium, making the Federation Planetary Development Council invest in the construction of a dilithium mining facility. The planet however was revealed by Leila Kalomi to be difficult to terraform to habitable conditions so the council decided to abandon further colonization efforts and automate the station instead.
Unknown to the team the planet was actually an artificial construct designed to imprison a powerful entity named S'uora that once controlled a powerful empire during an unknown period of time in galactic history. Eventually its servants managed to free themselves from S'uora's control and rebelled against it. After defeating the being it was imprisoned in a containment web of dilithium that drained its telepathic abilities. The planet itself had formed around this dilithium web.
Just prior to Stardate 5862.5, S'uora sought to escape the planet by mentally controlling the geologist Alan Becker, who was studying the nature of the dilithium deposits on the planet. His wife Leila Kalomi contacted Mr. Spock, an old friend of hers to come to her aid.
Soon after arrival, Mr. Spock learned of the true nature of the planet after encountering S'uora. He rescued both Alan Becker and Leila Kalomi from its control and brought them back to the surface so that the Enterprise's medical staff could treat the two.
After Captain Kirk informed Starfleet Command about the nature of the planet and its prisoner it was put under strict quarantine, forbidding any ship from travelling to it for at least a century. (TOS comic: "The Hollow Man")