Shards of the Shattered Pact: Seowyn's Crossing
Dagon is a powerful demon lord, lieutenant to the demon prince Demogorgon. According to some legends, Dagon was already in the Abyss when Demogorgon arrived. This supports the theory/belief will that the Abyss existed before the seed of evil was planted by the Nameless, which would suggest that the seed merely opened a door to the Abyss, rather than creating it.
Dagon is a huge, undersea entity, and he is calculating and cunning. He is rarely worshipped by mortals, but many pirates and seafarers of a darker nature will sacrifice to Dagon before they set out on a journey, to prevent the demon lord from sinking their ship or to persuade himn to guide fat vessels to their clutches. In fact, the term “Dagon’s Gullet” is often used by sailors to refer to the realm below the waves.