Fionn or Finn is actually a nickname meaning "fair" (in reference to hair colour), "white", or "bright". His childhood name was Deimne, and several legends tell how he gained the nickname when his hair turned prematurely white. The name "Fionn" is related to the Welsh name Gwyn, as in the mythological figure Gwyn ap Nudd, and to the continental Celtic deity Vindos.
The 19th century Irish revolutionary organization known as the Fenian Brotherhood took its name from these legends. The Scottish name Fingal comes from a retelling of these legends in epic form by the eighteenth century poet James Macpherson.
Muirne was already pregnant, so her father rejected her and ordered his people to burn her, but Conn would not allow it and put her under the protection of Fiacal mac Conchinn, whose wife, Bodhmall the druidess, was Cumhall's sister. In Fiacal's house she gave birth to a son, who she called Deimne.
The young Fionn met the leprechaun-like druid and poet Finn Eces, or Finnegas, near the river Boyne and studied under him. Finneces had spent seven years trying to catch the salmon of knowledge, which lived in a pool on the Boyne: whoever ate the salmon would gain all the knowledge in the world. Eventually he caught it, and told the boy to cook it for him. While cooking it Fionn burned his thumb, and instinctively put his thumb in his mouth, swallowing a piece of the salmon's skin. This imbued him with the salmon's wisdom. He then knew how to gain revenge against Goll, and in subsequent stories was able to call on the knowledge of the salmon by sucking his thumb.
The salmon's place in this tale displays the esteem in which this particular family of fish is held in many different mythologies. The particular species thought to be referenced in this tale, is the Salmonidae midlandus variant. This species held a special place of esteem in traditional Irish stories due to its strength, its appearance, (significantly more scales than other species, and therefore a more striking range of colours), and its relative scarcity. The story of Fionn and the salmon of knowledge bears a strong resemblance to the Welsh tale of Gwion Bach, indicating a possible common source for both stories.
In The Pursuit of Diarmuid and Gráinne, one of the most famous stories of the cycle, the High King Cormac mac Airt promises the now aging Fionn his daughter Gráinne as his bride, but Gráinne falls instead for one of the Fianna, Diarmuid Ua Duibhne, and the pair runs away together with Fionn in pursuit. The lovers are aided by Diarmuid's foster-father, the god Aengus. Eventually Fionn makes his peace with the couple. Years later, however, Fionn invites Diarmuid on a boar hunt, and Diarmuid is badly gored by their quarry. Water drunk from Fionn's hands has the power of healing, but when Fionn gathers water he deliberately lets it run through his fingers before he gets back to Diarmuid. His grandson Oscar threatens him if does not bring water for Diarmuid, but when Fionn finally returns it is too late; Diarmuid has died.
In Newfoundland, and some parts of Nova Scotia, "Fingal's Rising" is spoken of in a distinct nationalistic sense. Made popular in songs and bars alike, to speak of "Fingle," as his name is pronounced in English versus "Fion MaCool" in Newfoundland Irish, is sometimes used as in lieu of Newfoundland or its culture.
In Manx folklore, Fionn is a giant known as Finn MacCooill. One story says that he came to live in the Isle of Man, whereupon a Manx buggane came to fight against the famous Irish giant. Wanting to avoid a fight, Finn hid in the cradle while his wife entertained the buggane, pretending her husband was the baby and trying to scare off their visitor. She gave the buggane a griddle-cake with the iron griddle hidden in it, which he could not eat, and told him that her husband always ate such cakes. Then she gave a second cake to Finn, who easily ate it. Seeing that even the 'baby' was so strong, the buggane thought better of his fight and slunk off. However, later the two did meet and had a great battle at Kirk Christ Rushen. Finn's feet carved out the Channel between the Calf of Man and Kitterland, and the other channel between Kitterland and the Isle of Man. The buggane's feet at Port Erin made the opening for the port there. At last the buggane got the upper hand and the injured Finn had to flee. Finn could walk on the sea, but the buggane could not. Unable to follow, the buggane tore out a tooth and flung it after Finn, where it struck him and fell into the sea to become the Chicken's Rock. Finn turned and shouted a curse on the rock, which is why it is such a hazard to sailors.
In 1761 James Macpherson announced the discovery of an epic written by Ossian (Oisín) in the Scottish Gaelic language on the subject of "Fingal" (Fionnghall meaning "white stranger": it is suggested that Macpherson rendered the name as Fingal through a misapprehension of the name which in old Gaelic would appear as Finn). In December 1761 he published Fingal, an Ancient Epic Poem in Six Books, together with Several Other Poems composed by Ossian, the Son of Fingal, translated from the Gaelic Language. His cycle of poems had widespread influence on such writers as Goethe and the young Walter Scott, but there was controversy from the outset about Macpherson's claims to have translated the works from ancient sources. The authenticity of the poems is now generally doubted, though they may have been based on fragments of Gaelic legend, and to some extent the controversy has overshadowed their considerable literary merit and influence on Romanticism.
A story of the battle between Fionn MacCumhail, who in this tale is claimed to have resided in the valley of Glencoe, in Scotland, and a Viking host led by Earragan makes an appearance in the book Glencoe: The Story of the Massacre, Secker & Warburg, 1966 by John Prebble. The story tells of the approach of forty Viking galleys up the narrows by Ballachulish into Loch Leven, and the ensuing battle between the Norsemen and the Feinn of the valley of Glencoe, in which Earragan is slain by Goll MacMorna.
Fionn mac Cumhaill features heavily in modern Irish literature. Most notably he makes several appearances in James Joyce's Finnegans Wake, and some have posited that the title, taken from the street ballad "Finnegan's Wake", may also be a blend of "Finn again is awake," referring to his eventual awakening to defend Ireland.
Fionn also appears as a character in Flann O'Brien's comic novel, At Swim-Two-Birds, in passages that parody the style of Irish myths. Morgan Llywelyn's book Finn MacCool tells of Fionn's rise to leader of the Fianna and the love stories that ensue in his life. That character is celebrated in "The Legend of Finn MacCumhail", a song by the Boston-based band Dropkick Murphys featured on their album Sing Loud Sing Proud!:
Lord of the Celts is a dramatic musical program that was loosely based on the "Fionn and Sadbh" story from the Fenian Cycle of Irish mythology. The program was produced by the Radio Tales series for National Public Radio. This version was produced and script edited by series producer Winnie Waldron, who also served as the on-air host. The program was narrated by actress Winifred Phillips, who also wrote the script and composed the musical score. The program aired in the United States via NPR Playhouse on December 1, 1998, and currently airs in reruns on Sonic Theater channel 163 of XM Satellite Radio.