Fionn Mac Cumhail is a hunter-warrior and a hero in Irish mythology. He is the leader of the Fianna group of hunter-warriors comprised mostly of young men. Fionn is also portrayed as a talented prophet and poet, with a burnt, magic thumb that is said to grant him immense wisdom. He wields a sword, known as the Mac Au Luin, and is depicted having a pack of hounds that he hunts with. He was raised under the poet Finnegas, and was raised by druids. Fionn was prophesied to eat the Salmon of Knowledge, which he was tasked with catching and cooking. While doing so, he burnt his thumb on the fat, causing him to instinctively put it to his mouth. it imbued him with the salmon's wisdom, and increased his power thousandfold.
Etymology
Fionn's name, which in Old and Middle Irish is Find or Finn respectively, means a variety of things, primarily "white, lustrous, bright, fair, handsome, blessed, bright, moral, fair, true, and just."
His sword, with the epithet Mac Au Luin, translates directly to "The son of the waves".