Pholtus

Pholtus is the god of light, not the sun, like Pelor, or fire, or anything adjacent to light, but light itself. He's one of the older gods, and is taken from the Greyhawk Pantheon, but with a pretty heavy OC twist.

Pholtus' worshippers and cultists are called Pholtans.

They differ from most of the other pantheons in the setting in two respects: first, they are actually monotheist. Their doctrine is that Pholtus is the only real god, and everyone else is just jumped up spirits and wizards playing pretend. Second, they are way less tolerant of weird beliefs in their followers. Most everyone else will roll with heresy or strange syncretic stuff unless it's really out there, while Pholtans have an actual list of things that are allowed.

Of course, that means that there are a ton of Pholtan heresies, and they're pretty important both to the setting and this campaign in particular.