Finnegas is a legendary Irish poet and Sage according to the Fenian Cycle of Irish Mythology. He is the teacher of Fionn Mac Cumhaill, according to the tale The Boyhood Deeds of Fionn. For years he tries to catch the Salmon of Wisdom, a fish that will grant all the world’s knowledge to whoever eats it.
He is unsuccessful until he takes the young Fionn as his charge, but when Fionn cooks for him, he burns his thumb and puts it in his mouth. He therefore receives the fish’s knowledge, which he can access by putting his thumb in his mouth again.
Upon eating the salmon he recommends Finn take up the name Finn to fulfil the prophecy as to who will gain its wisdom, originally he was named Demne. As well as being renowned for his skills in composing and reciting poetry Finnegas knew more about the ways of the world, including the secrets of the birds and animals and plants and stars, than any other man in Ireland.