Clavicus Vile
Clavicus Vile is the Daedric Prince whose sphere is the granting of power and wishes through ritual invocations and pact. Clavicus has a companion named Barbas. While capable of selective shapeshifting, the form it assumes most of the time is that of a dog. Clavicus himself is depicted as a small jovial fellow with horns protruding from his forehead. He is aptly described as a Daedra who likes souls for the sake of having them.
For more information, see the article on Clavicus Vile.