In demonology, Marchosias is a great and mighty Marquis of Hell, commanding thirty legions of demons. In the Ars Goetia, the first book of The Lesser Key of Solomon (17th century), he is depicted as a wolf with gryphon's wings and a serpent's tail, spewing fire from his mouth, but at the request of the magician he may take the form of a man. He is a strong fighter and gives true answers to all questions, and is very faithful to the magician in following his commands. Before his fall he belonged to the angelic order of Dominations (or Dominions), and when he was bound by Solomon he told him that after 1,200 years he hoped to return to Heaven ("unto the Seventh Throne").
In the Pseudomonarchia Daemonum (1577) of Johann Weyer the demon is called Marchocias and his description is much the same as that given in the Goetia except that his gender when appearing as a wolf is female ("a cruel she wolf") and spewing forth "I cannot tell what" from his mouth. He likewise hopes to eventually return to the Seventh Throne but is "deceived in that hope."
Collin de Plancy in his Dictionnaire Infernal (1818) draws on both sources for his description of Marchosias in his catalogue of demons.
The name Marchosias comes from Late Latin marchio, "marquis".