Fionn mac Cumhaill, often anglicized Finn McCool or MacCool, is a hero in Irish mythology, as well as in later Scottish and Manx folklore. He is the leader of the Fianna bands of young roving hunter-warriors, as well as being a seer and poet. He is said to have a magic thumb that bestows him with great wisdom. He is often depicted hunting with his hounds Bran and Sceólang, and fighting with his spear and sword. The tales of Fionn and his fiann form the Fianna Cycle or Fenian Cycle, much of it narrated by Fionn's son, the poet Oisín.

Oisín, Osian, Ossian, or anglicized as Osheen was regarded in legend as the greatest poet of Ireland, a warrior of the Fianna in the Ossianic or Fenian Cycle of Irish mythology. He is the demigod son of Fionn mac Cumhaill and of Sadhbh, and is the narrator of much of the cycle and composition of the poems are attributed to him.