One of the two races that originally inhabited the planet Skaro, their descendants became the Daleks, after they were mutated by a brief nuclear war between the Dal and Thal races some '500 years ago'. This race of Daleks was supposedly destroyed when their power supply was wrecked. Somehow however this version of time became corrupted and changed, the Daleks survived and the Dal race was eliminated from Time and Space, to be replaced by the Kaled.

At least that was what the Time Lords recorded until Sallerman Caan was encountered on Castris Sigma (Episode 4: To Dream of the Daleks.