Anyone know of a good demonologist core class?

[yennico]

A good question but I was looking for a little more differentiation than just a Cleric with the appropriate domains. Otherwise there is little/no difference from a demon worshiper and an evil deity worshiper.

There is a diffenece between an evil deity worshiper and a demon worshiper.
An evil deity needs his worshipers because the power of a deity is related to the number of worshipers. A demon lord do not needs his worshipers, he even exists without any worshiper.
A demon lord and a deity can only grant spells thye know. Most deities know more spells than a demon lord. Some demon lords do not know spells of cerrtain areas (e.g. healing).
A deity grants his worshipers his powers without a price. A demon IMHO grants the powers to his worshipers only for a price.
An intelligent demon lord do not want to walk on the material world because this will cause a union of powerful mortals against him and some deities also will interact, but the demon lords loves to send his demonic minions on the material plane.