The Fenian cycle (an Fiannaíocht) is also called the Fionn cycle (after the main character Fionn Mac Cumhaill) or Ossianic cycle (after his son and narrator Oisin).
This collection of poems, tales and ballads covers the deeds of the legendary Finn McCool (MacCumhaill) and the Fianna in the reign of Cormac mac Airt in Ireland 3rd century AD. The Fenian cycle contains many of the best-loved Irish folk tales, a collection of old manuscripts such as The Book of the Dun Cow (c. 1100) and The Book of Leinster (c. 1160) and The Interrogation of the Old Men.
The Fenian Cycle is about the Fianna and the central character of Fionn Mac Cumhaill, and The Boyish Exploits of Finn (Macgnímartha Finn) gives the background of the great leader of the Fianna.
Set in the time of King Cormac Mac Airt, it’s said he created the Fianna from clans all over Ireland. The two notable were Clann Baíscne of Leinster led by Cumhail and Clann Morna of Connacht, led by Goll mac Morna. The rival clans were the most powerful, but ultimately Cumhail led the Fianna much to Goll’s distain. Now I’m a stickler for a timeline, so feel it prudent to point out that Cormac Mac Airt was the son of Art mac Cuinn, himself a High King and the son of Conn Cétchathach, the first High King of Ireland, better known as Conn of the Hundred Battles. So when the story says it was Conn’s army that killed Cumhaill at the Battle of Cnucha, when his grandson supposedly set up the Fianna when he was High King, it doesn’t really add up. Unless of course Cormac was simply a king and his grandfather the High King. Either way, the High Kings resided at the Hill of Tara, and the slaying of Aillen by Fionn results in High King Cormac gifting him leadership of the Fianna.
Either way, the Boyhood Deeds of Fionn tells us that his mother was Muireann Muncháem (Muirne), daughter of druid Tadg mac Nuadat, who lived on the hill of Almu. He spurned any potential suitor after he had prophecised that her marriage would result in losing his home. Cumhal had fallen in love with her so abducted her. Outraged, Tadg went to the High King of Ireland, and Conn of the Hundred Battles forbade the relationship and his troops fought Cumhall at the Battle of Cnucha. Cumhal was killed by Goll Mac Morna, who took over the leadership of the Fianna.
A pregnant Muraine was returned to her father, who outraged and shamed, rejected her and sentanced her to death.King Conn stopped this and sent her to the Cumhal’s sister, Druidess Bodhmall.
Muireann gave birth to a son called Deimne, and she left her son to protect him with Bodhmall in Sliabh Bladhma, Laois, the Slieve Bloom Mountains).
Deimne was brought up in secret by his two foster mothers, Bodhmall and her companion Liath Luachra, a great warrior. They taught him how to be a great warrior, and he became Fionn mac Cumhaill.
Key Stories of the Fenian Cycle
The Boyhood Deeds of Fionn
Fionn and Aillén
Fionn and Sadhbh
Fionn and Diarmuid
The Battle of Gabhra
Tir na Og
Also known as the Finn Cycle, and Ossianic Cycle after its narrator Oisín (son of Finn McCool), it contains stories about the nomadic Fianna and their leader Fionn mac Cumhaill. Stories about notable Fianna members include Goll mac Morna, Caílte, Diarmuid, Oscar (son of Oisín).