The Beta Thoridor planet was a planet in the Beta Thoridor star system. After the Klingon Empire conquered Beta Thoridor in the 2220s, the planet became a subject world of the Empire. Beta Thoridor's system was a theater of operations during the Klingon Civil War, and was later again besieged during the Borg Invasion of 2381. In 2381, all life on the world was exterminated. (ST novel: Mere Mortals)