In demonology Gusion is a strong Great Duke of Hell, 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 honour and dignity.

He is depicted as a cynocephalus.

Other spellings: Gusoin, Gusoyn.

See also The Lesser Key of Solomon, Ars Goetia.