Let's meet one face of Ireland's Fire God: Áed, appearing in one of his saintly forms as Máedóc of Ferns. We'll need a few other saints to properly introduce him, though.
The Fire God is at once a really central god, because they turn up everywhere, but also quite subtle, being rarely the main character. Cosmogonically, "Fire" can be a key aspect of the proto-creator "Cosmic Person" figure, and can then later turn up in more specific manifestations. Fire can have multiple distinct aspects; Fire of the Sun, Fire of the Heavens (lightning, aurorae, etc.), the Fire of Earth, and perhaps the Fire of Stone or Water. This can make it a mess to find and figure out the "Fire God": Which one? Do they share a common top-level identity?
I mentioned in Féichín's issue that the Fire-Deity has an unexpected face: Manannán mac Lir. He's been assumed for centuries to be a sea deity like his father, Ler. It's confusing to our modern sensibility, but to Bronze / Iron age societies, Fire was not seen as the antithesis of Water. I'll give this some attention in the "Patterns" section, below. By comparison though, it's a sure thing: Hephaestus grew up underwater, Vedic Agni is repeatedly called "of the waters", and Loki (a Norse putative fire deity) is quite comfortable in water.
Manannán is not the only Fire God - it's long-speculated that at least one "Áed" (literally meaning "Fire"), a son of The Dagda, may have been an Irish fire deity. Today's saint, Máedóc (and a few other Áeds besides), will help bolster that case, by exhibiting parallels with the mythic attributes of Manannán. But this won't be the last major saint that lines up with Manannán. And, it's not all about Manannán either - there's a lot here to show other faces of Fire not before seen in the Mythological material.