Fionn was the son of Cumhail who, on fighting for the position of leader of the Fianna, a warrior body of ancient Ireland who guarded the High King. Cumhail, was killed. His wife feared for their son’s life, so she sent him away to be raised by a Druidess and her sister who were strong and wise women.
A druid, Fingeas, caught the Salmon of Knowledge and gave it to Fionn to cook. As he was cooking it, Fionn burned his thumb and sucked it, in the process acquiring the gift of prophecy.
Fionn uses his gift wisely and gains command of the Fianna by saving the life of the High King Cormac who then promises his daughter, Gráinne, to him as his wife. Fionn turns the Fianna from an unruly mob of fighters into a highly respected elite who were meant to be models of chivalry.
One of the best known of Fionn’s legends is that he is responsible for the formation of the Giant’s Causeway in Co. Antrim: A Scottish giant named Angus has cast aspersions on Fionn’s fighting prowess. Fionn throws a rock into the sea, challenging Angus to a fight. The two giants begin to build a pathway across the sea to fight each other. But Fionn is concerned because Angus is supposed to be twice his size. The night before the causeway is finished and the fight will take place, Fionn and his wife Una make giant baby clothes and a giant cradle. Fionn gets into the cradle in the baby clothes. Angus arrives at Fionn’s castle where Una shows him Fionn masquerading as a baby. The Scottish giant is now terrified as he thinks that if this is the baby, Fionn himself must be a monster. He runs away, back across the causeway, with Fionn in pursuit, lumps of earth being pounded out of the ground after him. One of the holes that he creates is filled with water and becomes Lough Neagh, the biggest lake in Ireland. Another lump falls into the Irish Sea and becomes the Isle of Man.
According to folklore, Fionn MacCumhail is not dead but sleeping in a cave, waiting to defend Ireland should the need arise….