Among the demons in Colin de Plancy’s 1818 Dictionnaire Infernal are many creatures who bestow knowledge or other boons on mortals willing to make a deal with them.
One of these is stolas, also Stolos, a prince of hell. Like many powerful demons, he is a shapeshifter: when appearing before mortals, he first takes the form of either an owl or a great raven, before transforming into a human.
He is commonly depicted as a long-legged owl wearing a crown (presumably to denote his royal status in the infernal hierarchy). The image above is the illustration for his entry in the 1863 edition of the Dictionnaire Infernal.
When called upon, Stolas can teach his summoner about astronomy, which is his specialty. He is also knowledgeable about the values of precious stones and the properties of herbs and plants.
Stolas is the 36th demon listed in the Ars Goetia, one of the books in the 17th century Lesser Key of Solomon. It also has an illustration of his personal demonic seal (see image). Among the forces of hell, Stolas is a powerful commander, being the general of 26 legions of demons.
Though not as popular as names like Baal, Asmodeus and Belial, the crowned owl demon has inspired several characters in modern fiction, such as in Helluva Boss and Castlevania.
Collin de Plancy, J.-A.-S., 1863, Dictionnaire Infernal: répertoire universel des êtres, des personnages, des livres, des faits et des choses qui tiennent aux esprits, aux démons, aux sorciers, au commerce de l’enfer, aux divinations, aux maléfices, à la cabale et autres sciences occultes, aux prodiges, aux impostures, aux superstitions diverses et aux pronostics, aux faits actuels du spiritisme, et généralement à toutes les fausses croyances merveilleuses, suprenantes, mystérieuses et surnaturelles, Sixième Édition, H. Plon, 723 pp., p. 635-636.
De Laurence, L. W., 1916, The Lesser Key of Solomon: Goetia: The Book Of Evil Spirits, Literary Licensing, 90 pp.
(Image source 1: Thiago Lehmann on Artstation)
(Image source 2: Louis le Breton, illustration for Dictionnaire Infernal, 6th edition, 1863)
(Image 3: the sigil of Stolas, from the Ars Goetia)