Zargon the Returner

Zargon the Returner is the god worshipped by the Guild of Hermits.

Prudence's adopted father Cyrus was a follower of Zargon the Returner, but that wasn't who she wanted to have as her patron, so she killed him and created a pact with Cthulhu.

Description
Zargon the Returner is a god that wishes to drown the world in slime, but his powers seem limited in a way that he can only affect those who worship him. He also apparently hates it when people get his name wrong.