Leonard is a demon or spirit in the Dictionnaire Infernal, grandmaster of the nocturnal orgies of demons. He is represented as a three-horned goat, with a black human face. He marks his initiates with one of his horns. Infernal powers obtained from the worship of Master Leonard range from metamorphosis into monstrous animals or men to flight as an Incubus.
There is mention of a "Master Leonard" in the Dictionary of Phrase and Fable in association with the alleged deity of the Templars, the Baphomet or "Goat of Mendes." Black banquets are thrown in Leonard's honor where aborted kid goats are eaten without salt and boiled with reptiles to sully the sinless nature of the clean meat.
Leonard has been known to take other forms, and there is some connection to the legend of the werewolf; he has been known to appear as a handsome soldier, a favorite of many demons. In this form he will seduce a young lady and take her to the wilderness where he will lay with her. Any child resulting from this union will be stillborn, an offering for sin.
Leonard is the leader of the Deva Cult in Ueno, and holds many sabbaths there. Once the hero has the Inverted Cross dropped by Apollyon, he can visit Ueno while the moon is full and witness one of Leonard's sabbaths. A battle will start, and Leonard will summon three groups of demons to fight for him. After defeating the 3 groups of demons he summoned, he will take that as an "insult to the great Leonard" and fights the hero. Once he is defeated, the hero will receive the Jupiter Pillar and the human members of the Deva Cult are freed from their brainwashing.