Fionn or Finn is actually a nickname meaning "fair", a reference to hair colour (in some variations, it may also mean "white," a reference to purity).
Fionn was the son of Cumhail, leader of the Fianna, and Muirne. When he was just a baby, due to his father's death at the hands of his rival, Goal mac Morn, his mother chose to send him into hiding in the woods, in the care of two women: Bodhmall, a Druid, and Liath Luachra, a warrior and trainer. In the care of these two women he was given an extensive education in the subjects considered important for an Irish youth of his caste and time. When old enough, he returned to society, and passed the extraordinary tests required for membership in the Fianna. Fionn tried to serve several kings but they refused, frightened of retaliation from Goal.
Finally, Fionn met a poet near the river Boyne and studied under him for seven years. Near the end of the seven years, the poet caught the Salmon of Knowledge and Fionn cooked it for his master, not knowing the power of the fish. While it cooked, he burst a blister on the salmon, which burned his thumb; Fionn then sucked his thumb. As piece of the salmon's skin had become attached to his thumb, which Fionn then swalled, he inherited the wisdom of the salmon. He then knew how to gain revenge against Goal, and in subsequent stories was able to call on the knowledge of the salmon by sucking his thumb.
In one version of the tale, Fionn killed Goal and the rest of his men; in another, he humbled Goal, who later became one of his most trusted soldiers.
Fionn eventually married a Sidhe woman.
Alternative: Fionn, Finn, Fionn mac Coul, Fionn mac Cool, Finn mac Coul, Finn mac Cool, Finn mac Cumhail, Finn McCool.Legend