The Celtic gods of the dead were Gwynn ap Nudd for the British, and Arawn for the Welsh. This idea is based on a fallacy that seems to have come from Col. Charles Vallency's books in the 1770s before the reliable translations of existing Celtic literary works and before archaeological excavations. Samhain is the name of the holiday. This is an important distinction, for Halloween's association with Satanic worship is a modern phenomenon. It is important to distinguish between paganism and Satanism.
Pagans are people who believe in more than one god.
Some modern day pagans call themselves Wiccans . Pagans are quick to emphasize that they do not worship Satan or the devil. Celts were pagans, not Satanists. Of course, from a Christian standpoint both are in error. There is no original evidence to indicate that Samhain was any more Satanic than pagan harvest festivals of other religions, like the Romans or the Greeks.