An early form was a nickname for a hairy person, from the Middle High German rūch, rūhe, rouch, meaning hairy, shaggy, or rough.
[1] As a surname, it was first found among notable families in Saxony in the 13th century.
[1] This derived from the Old Norse personal name "Radulfr", composed of the Germanic elements rad (meaning counsel or advice), and wolf (wolf).
The variant form "Rau" was reintroduced into England by French Huguenot refugees in the late 16th century.
In France, it was a variant form of the surname Rheault, of French or Breton origin.