Necros was a human-colonised planet and the location of Tranquil Repose, the finest funeral home in the galaxy. It was also the location of Kara's food-processing factories, which provided food for starving planets; as it turned out, however, the food was actually made from humans that had been placed in Tranquil Repose. The product was manufactured by Davros, who called himself "the Great Healer".
The official colour of mourning on Necros was blue, and women's legs were to be covered at all times. The planet was cold, and home to dangerous creatures such as the voltrox and speelsnape. The weed plant was the only plant that grew on Necros and provided protein when refined.
Davros took over Tranquil Repose to hide from the faction he called the Renegades, led by the original Dalek leader, the Supreme Dalek. He was later found and taken by them for a trial. (TV: Revelation of the Daleks)