In demonology Forneus is a Great Marquis of Hell, and has twenty-nine legions of demons under his rule. He teaches Rhetoric and languages, gives men a good name, and makes them be loved by their friends and foes.

He is depicted as a sea-monster.

His name seems to come from Latin 'fornus', 'furnus', oven.

See also The Lesser Key of Solomon, Ars Goetia.