The twelfth planet in a solar system not too far from Earth. Skaro was the home world of both the Kaleds and the Thals. It was ravaged by the neutronic wars between the two races, which made it largely radioactive. The Kaled scientist Davros further developed some of the mutations, created a mobile casing for them and christened them Daleks. The Time Lords sent the Fourth Doctor to Skaro to stop the development of the Daleks, but he failed, succeeding only in entombing them in the Kaled bunker, after they had turned against their creator (4E).
Later, some crippled Kaled survivors discovered the remnants of Davros' early experiments and mutated themselves into new Daleks. The First Doctor met the new Daleks in the Dalek City and foiled their attempt to destroy the surviving Thals by increasing Skaro's radiation levels. Those new Daleks presumably perished when the Thals destroyed their power controls (B).
The original Daleks ultimately resurfaced and took over Skaro, driving the Thals away. They then ruled over Skaro (K, EE, KKK, XXX) until the planet was again reconquered and occupied by the Thals (QQQ, SSS). Skaro was eventually ravaged by further warfare between the Thals and the Daleks, and became a dead planet. By then, the Daleks had emigrated to another world (herein dubbed "Skaro II"). The ultimate fate of the Thals remains unknown.
The Daleks returned to the original, ravaged Skaro to find their creator, Davros, so that he could help them in their fight against the Movellans (5J). The Daleks and Davros then fought for control over the Dalek species (6P, 6Z). Eventually, either the original Skaro's, or Skaro II's, sun was turned into a supernova when Davros, against the Seventh Doctor's advice, used the Hand of Omega (7H).
However, the Daleks continued to plague Mankind from Skaro (or Skaro II?) (R, T/A, V). It was there that the battle between the Daleks and the humanized Daleks engineered by the Second Doctor took place, putting a final end to the Daleks' history (LL). The Varga plants (T/A) and the Slyther (K) were lifeforms indigenous to Skaro.
See D5 GAMMA Z ALPHA