Sontar

Sontar was the home planet of the Sontarans. Its name was included in the Sontaran battle chant, "Sontar, ha." (DW: The Sontaran Stratagem) Circa the 25th or 26th century, the Sontarans' enemies, the Rutans destroyed Sontar with photonic bombs, leading to the dispersal of Sontaran troops across their home galaxy of Mutter's Spiral. (DWM: Pureblood) In the episode Turn Left it was mentioned that in Donnas parallel universe Captain Jack Harkness was forced to teleport himself to the Sontaran homeworld in order to escape the explosion when the Tenth Sontaran Battle fleets ship was blown up.

Other information
The supreme military of the Sontaran Empire, General Sontar, had the same name as the planet.