Thallus was a planet in the Thallus system, located in Federation space just outside Klingon Empire territory in the galaxy's Alpha or Beta Quadrant. It was the homeworld of an advanced civilization.
History and specifics[]
Thallus was the site of a prison. Prior to 2273, Raytag M'Gora escaped from it, but was eventually recaptured and detained at a facility on Earth.
In 2273, Thallus natives opened diplomatic relations and wished to join the Federation. Ambassador R'Kgg was sent to begin negotiations, and headed there with M'Gora aboard the starship USS Enterprise. En route, however, R'Kgg was killed. (TOS comic: "The Haunting of Thallus!")
A few hours prior to assuming orbit, the Enterprise was diverted by Klingons to an orbiting prison satellite, which turned out to be a space station disguised as a floating haunted house. A Klingon thought enhancer embedded in M'Gora overloaded and killed him. Instead of continuing on to Thallus, the Enterprise brought M'Gora's body to Starbase 16. (TOS comic: "The Haunting of the Enterprise!")