Home planet of the Daleks, as well as the Thals and the Kaleds, two races who were at war for over a thousand years. A third group called "mutos" were mutant Thals and/or Kaleds forced to live in exile. A Kaled scientist called Davros engineered the Daleks who went on to exterminate the whole of both races (except for Davros himself, though they tried)and eventually became an interstellar empire. Skaro was destroyed by the 7th Doctor, somehow brought back or replaced, and again destroyed, presumably, during the Last Great Time War
Skaro is a planet, so don't say a Skaro.