Samhain: The Celtic New Year.
There are many gods associated with Samhain; this list could be endless. A smattering is as follows:
The Dagda: The Irish All-Father, the Good God. In some thought, he has been associated with Samhain.
Echoed Voices: The Dagda - October 2002
Lugh: The Irish Many-Skilled God. The Main God of the Tuatha De Danaan. I've seen many references to Samhain being His day, when He goes to rest after being overthrown (?). But I'm still undecided about this one... But... for what it's worth. Add Lugh to the list.
The Morrigan: The Irish Goddess of Sovereignity, and war. Of course with that distinction, She/They (as threefold goddess: Morrigan/Babd/Fand) could easily be associated with Samhain.
Puca? An Irish mischievous Sidhe that comes out to play, so to speak, at Samhain.
The idea that there is a supposed God named "Samhain" has, I think, been sufficiently debunked. I've never run across it, in my studies... or not yet.
Pwyll? Welsh god of the Underworld.
Rhiannon? Welsh Goddess of Horses, Love, Wife of the Underworld god Pwyll?
I'm sure there are many more I am forgetting. Anyway, there are just a few to pique your research interest.
More to come...