Demonolaters are priests who serve demon lords and ladies. The character class is a sub-class of cleric, but each demon lord has priests with special powers and spells, nearly 40 of which are included (with names like dark offering, invite possession, and warp reality).
This supplement also includes rules for demonic pacts and statistics for the demon lord Dagon and his minions, the dreaded carcharo demons.
You can buy the Demonolater on its own for just $4.25, or if you've been holding out for a collection of all three Darker Paths books (the Necromancer, the Witch, and now the Demonolater), you can get a bundle for just $9.95 (that's around 30% off the individual price!).