Pure-blood was a term referencing wizarding families or individuals descended only from magic, with no Muggles, Squibs or Muggle-born witches or wizards in their family. The concept was first popularised by Salazar Slytherin who campaigned to keep Hogwarts exclusively for pure-blood families. Although this stance became less mainstream, for some families, in particular the Gaunts, Lestranges and Blacks, an adherence to pure bloodlines remained important and they continued to marry within a very small pool. These families tended to be sympathetic to Dark wizards and had a history of support for the likes of Gellert Grindelwald and Lord Voldemort.