Got the idea to do this because of a few things I have seen in pagan tags and the “celtic” tag. I think it’d be useful to talk about a bit, so that everyone has the vocabulary to distinguish between gods who might be calling them, different things that interest them, etc.
Celtic is an umbrella term that covers a wide variety of cultures. The most important thing to learn about the word “Celtic” is that it does not, on its own, describe anything. It is only an umbrella term. Think of it as an adjective without a noun. There are many Celtic cultures, many of which (but not all!) speak Celtic languages. The term “Celtic” usually refers to language groups above all things. While there are many awesome and fascinating modern Celtic cultures, since this is a pagan blog, we’re going to talk about ancient polytheistic Celtic cultures. What is important to note here is that Celtic cultures are not interchangeable with each other. Each has a unique culture, unique deities, unique religious practices, and was culturally distinct from its neighbors, both Celtic and non-Celtic. This is the most important part. I often see people asking about “The Celtic Pantheon,” and I usually can’t help them very well because there was no such thing… There are, however, many individual pantheons that a person might be interested in:
Deities and heroes you may know: The Morrigan, the Daghda, Aoife, Fionn MacCumhaill, Dierdre, Lugh, Cuchulainn (more complete list of Irish mythological figures)
Language: Scottish Gaelic
Deities and heroes you may known: Shared with Ireland, but with local alterations to folklore and especially folk practice (Scottish Mythology on Wikipedia)
Deities and heroes you may know: Arianrhod, Rhiannon, Pwyll, Arawn, Gwyn ap Nudd, Mabon, Lleu Llaw Gyffes, and many early versions of Arthurian figures (Welsh Mythology on Wikipedia)
Language: Brittonic or Gallo-Brittonic
Deities and heroes you may know: Nodens, Andraste, Brigantia, Toutatis, Sulis (British Iron Age on Wikipedia)
Deities and heroes you may know: Cernunnos, Toutatis, Taranis, Esus, Lugus, Matrona, Rosmerta (Wikipedia unfortunately has no article on Gaulish religion but does have one on Gaul and a hub for Gaulish and Brittonic Deities; note that there is a small degree of crossover but also a high degree of native deities on both sides of the channel)
Celtic Iberia and Lusitania
Language: Celtiberian, Lusitanian
Deities you may have heard of: Bandua, Endouellicus, Ataegina (Lusitanian Mythology on Wikipedia)
I have barely scratched the surface here with this overview, but I hope that it was helpful and informative! With any luck, it will give those interested some useful jumping off points to begin research and learning.