Fionn mac Cumhaill

Fionn mac Cumhaill is the leader of the Fianna and the central hero of the Fenian Cycle. Born Deimne, son of Cumhall (a former leader of the Fianna killed by rivals before Fionn's birth), he is raised in hiding by two women, a druidess and a warrior, who train him in the skills he will need to eventually reclaim his father's position. The most famous story of his youth concerns the Salmon of Knowledge. While studying poetry under the poet Finnegas, who has spent years trying to catch a salmon said to grant all the world's knowledge to whoever eats it, the young Fionn is given the task of cooking the salmon once it is finally caught, with strict instructions not to eat any of it himself. While turning the fish, he burns his thumb on its skin and instinctively puts the thumb in his mouth to ease the pain — accidentally receiving the salmon's wisdom instead of Finnegas. For the rest of his life, Fionn can access this boundless knowledge at will simply by biting his thumb, a gesture that becomes his signature source of insight throughout the cycle. As leader of the Fianna, Fionn presides over a band admitted only through severe trials — a candidate had to be a master poet, able to defend himself unarmed while buried to the waist, and able to run through a forest at full speed without breaking a single fallen branch underfoot, among other tests. Fionn's own story is deeply tied to those of his family and companions: his son Oisín becomes the Fianna's great poet, and one of the cycle's most painful episodes involves his intended bride, Gráinne, fleeing with the younger warrior Diarmuid on their wedding day, launching a pursuit that runs through much of the wider Fenian material. Tradition holds that Fionn did not truly die, but sleeps in a cave with the Fianna around him, ready to rise again if Ireland ever needs them.