In demonology, Gusion is a strong Great Duke of Jinnestan, and rules over forty (forty-five according to other authors) legions of demons. He tells all past, present and future things, shows the meaning of all questions that are asked to him, reconciles friends, and gives honor and dignity.
He is depicted as a baboon or according to some, in the form of an Xenophilus.
Other spellings: Gusoin, Gusoyn.
He is mentioned in The Lesser Key of Solomon