From an original 1863 Louis le Breton's illustration
Amdusias (also spelled Amduscias and Amdukias) is one of the Demons of hell described in the Goetia, one of the books of the manuscript grimoire known as the Lemegeton or Lesser Key of Solomon. He is mentioned by Johann Wier in his Pseudomonarchia daemonum , and by Reginald Scot in The Discoverie of Witchcraft
In Collin de Plancy's illustration, Amdusias is crowned to show that he is a duke of hell. He has been given a horse's head to go with his single horn, because unicorns are usually represented in the shape of a horse. Two trumpets lie on the ground, and a third trumpet is slung over his shoulders.
(source: Demonologia, 2003)