The ancient druids chief god

There were two; the chief God and the chief Goddess. There were many, many different names - they varied between villages, sometimes, but it was generally the same two people:

First, there was the Great Mother; a threefold Goddess (three representations, three forms) known as Brigid (Brighid, Brigit) the Maiden, Modron the Mother, and the Old Wise Woman.

She represented and embodied the Celtic land and was honored as the greatest deity, the mother of all.

Then there was Dagda (Daghda, Daghdha) who was the God. He was the Father and embodied all that was 'good', good in the sense of being skilled at something, not the opposite of evil.