Fianna in the context of "Acallam na Senórach"

The Fenian Brotherhood (Irish: Bráithreachas na bhFíníní) was an Irish republican organisation founded in the United States in 1858 by John O'Mahony and Michael Doheny. It was a precursor to Clan na Gael, a sister organisation to the Irish Republican Brotherhood (IRB). Members were commonly known as "Fenians". O'Mahony, who was a Gaelic scholar, named his organisation after the Fianna, the legendary band of Irish warriors led by Fionn mac Cumhaill.

Irish mythology is the body of myths indigenous to the island of Ireland. It was originally passed down orally in the prehistoric era. In the early medieval era, myths were written down by Christian scribes, who Christianized them to some extent. Irish mythology is the best-preserved branch of Celtic mythology.

The myths are conventionally grouped into 'cycles'. The Mythological Cycle consists of tales and poems about the god-like Tuatha Dé Danann, who are based on Ireland's pagan deities, and other mythical races like the Fomorians. Important works in the cycle are the Lebor Gabála Érenn ("Book of Invasions"), a legendary history of Ireland, the Cath Maige Tuired ("Battle of Moytura"), and the Aided Chlainne Lir ("Children of Lir"). The Ulster Cycle consists of heroic legends relating to the Ulaid, the most important of which is the epic Táin Bó Cúailnge ("Cattle Raid of Cooley"). The Fenian Cycle focuses on the exploits of the mythical hero Finn and his warrior band the Fianna, including the lengthy Acallam na Senórach ("Tales of the Elders"). The Cycles of the Kings comprises legends about historical and semi-historical kings of Ireland (such as Buile Shuibhne, "The Madness of King Sweeny"), and tales about the origins of dynasties and peoples.

Fionn mac Cumhaill, - alternatively spelled Finn mac Cumhaill - sometimes anglicised 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 (an Fhiannaíocht), much of it narrated by Fionn's son, the poet Oisín.

The Fenian Cycle (/ˈfiːniən/), Fianna Cycle or Finn Cycle (Irish: an Fhiannaíocht) is a body of early Irish literature focusing on the exploits of the mythical hero Finn or Fionn mac Cumhaill and his warrior band the Fianna. Sometimes called the Ossianic Cycle /ˌɒʃiˈænɪk/ after its narrator Oisín, it is one of the four groupings of Irish mythology along with the Mythological Cycle, the Ulster Cycle, and the Kings' Cycles. Timewise, the Fenian cycle is the third, between the Ulster and Kings' cycles. The cycle also contains stories about other famous Fianna members, including Diarmuid, Caílte, Oisín's son Oscar, and Fionn's rival Goll mac Morna.