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." 
The name Marchosias comes from Late Latin marchio, "marquis".
In popular culture
In James Blish's apocalyptic novel Black Easter, black magician Theron Ware demonstrates his powers to sceptical arms-dealer Baines by performing a "sending" of Marchosias to cause the suicide by poison of an eminent physicist. The goetic ceremony of evocation is described with a vividness and a meticulous attention to detail unusual in a work of fiction.
Marchosias appears in the Legends of Tomorrow season 5 episode "Ship Broken", where he is a hellhound that was previously the dog of famed serial killer Son of Sam. He was taken from Hell by Gary Green and brought aboard the Waverider timeship, before nearly massacring the whole crew, only to be sent back to hell by John Constantine.
In Wolf's Curse by Kelley Armstrong, a demon claiming to be Marchosias appears with her hell beasts and she claims to be the creator of werewolves. This is said by a werewolf to be one of many legends as to their creation and that he doesn't know or care if the demon is actually Marochosias.
The ASW-G-35 Gundam Marchosias (ガンダムマルコシアス) is a mobile suit from the Mobile Suit Gundam: Iron-Blooded Orphans Urdr-Hunt mobile game   and is one of the 72 Gundam Frames created during the Calamity War.   
- S. L. MacGregor Mathers (trans.) and A. Crowley (ed.), The Goetia: The Lesser Key of Solomon the King (1904). 1995 reprint: ISBN 0-87728-847-X.
- Pseudomonarchia Daemonum