In demonology, Vepar is a strong Great Duke of Hell, and rules twenty-nine legions of demons. He governs the waters and guides armoured ships laden with ammunition and weapons; he can also make, if requested, the sea rough and stormy, and to appear full of ships. Vepar can make men die in three days by putrefying sores and wounds, causing worms to breed in them, but if requested by the conjurer he can heal them immediately.
Vepar is depicted as a mermaid. Despite this, he is always described with male pronouns, although this may be because words like "merman" were uncommon or not in use when Vepar was first described.