Before the Daleks arose, Skaro was the home of a humanoid species with two races, the Kaleds (or Dals) and the Thals. The races went to war with each other, using nuclear, chemical, and biological weapons that eventually caused mutations which Kaled scientists recognized as being the end of their species in its (ideologically defined) "pure" form. In events shown in Genesis of the Daleks, the Kaled chief scientist Davros accelerated their mutations and placed the now mutated Kaleds in tank-like "Mark 3 travel machines". These cyborgs became the dreaded Daleks (an anagram of Kaleds).
The Daleks eventually drove the Thals from Skaro, only to find themselves ruling a devastated planet, with dead seas and a surface nearly devoid of life. However, even the ravaged Skaro remained rich in minerals, which the Daleks used to build massive armies to conquer and destroy other worlds, eventually building the interstellar Dalek Empire. Some time afterward, the Daleks abandoned Skaro, though the planet was later reoccupied by the Imperial Dalek faction, apparently at the behest of Davros.
Skaro's final appearance in the classic series (in the chronology of the Doctor Who universe) is in the story Remembrance of the Daleks, in which the Seventh Doctor tricked Davros and his "pure Imperial Daleks" into stealing the Hand of Omega. As per the Doctor's prediction, the Daleks attempted to use it on Skaro's sun in order to generate enough energy to recreate the Gallifreyan time travel experiments. However, the Doctor had already pre-programmed the Hand of Omega to turn their sun into a supernova, resulting in Skaro's being completely obliterated.
At the start of the 1996 Doctor Who television movie, the Master is put on trial on Skaro by the Daleks and exterminated. Presumably this took place in the relative past of Skaro's timeline before its destruction, as the Eighth Doctor does not comment on it.
Skaro did not appear in any of the Dalek-related stories
