No, not Lucky C. Leprechaun, although he's important as well. I'm taking about the giant warrior Finn MacCool, who HAS to be cool, because it's in his name! Okay, a more accurate rendering of the Gaelic is Fionn mac Cumhaill, but it's PRONOUNCED "Finn MacCool."
Cumhaill is the name of his father, an Irish war leader, who eloped with the druid Tadg mac Nuadat's daughter Muirne shortly before dying at the hand of Goll mac Morna. Muirne left Finn to be raised by a warrior woman and a druidess. In his adult life, he became the leader of the Fianna in Goll's place. He gained the power of knowledge and prophecy by eating a piece of salmon skin, and performed many great deeds, including slaying a destructive fire-breathing fairy and saving a castle from an old hag and her sons. Like Paul Bunyan in American tall tales, he's also credited with creating some natural features in Ireland. The Giant's Causeway and Isle of Man supposedly came into being during a battle between Finn and a Scottish giant.