Before Canute, an ealdorman administered a shire of province for the King. In Latin documents he was styled Dux or Comes, taking the place between the royal Atheling and the thegn. Under Canute the Danish equivalent of Earl was introduced.
Under the Normans the government of an earl was normally restricted to one county and became hereditary, though losing the functions of the King's representation in the county to the sheriff. An earl was usually invested with the third penny out of the sheriff's court of the county, of Anglo-Saxon origin.
An Earl is styles Right Honourable, and is formally addressed by the Sovereign as Our right trusty and entirely beloved cousin (and counselor when the Privy Council).