The Adversary is an archetype found across cultures, manifesting as figures such as Satan, the Devil, Iblis, Mephistopheles, and Samael. Sometimes depicted as separate from God and other times an agent of them, this figure represents the inclination of evil in humanity.
A witch at her cauldron, standing in a magic circle, surrounded by demons. A grimoire (book of magick spells) can be seen in the right corner, and a goat, representing the Devil, can be seen behind her. Etching by Jan van de Velde II, 1626. Source: Wellcome Library
Dagol, The Prince of Darkness. The name Dagol doesn’t appear in any other grimoires or demonology books that I could find. His ‘Prince of Darkness’ designation leads one to believe it could be another name for Satan himself, however the demon Belial also bears that title. Though the source is quite old, it isn’t as old as it purports to be and was likely created for resale as a rare book, not as a genuine grimoire. Compendium Of Demonology and Magic, 1775.