The Gaelic hero Fionn mac Cumhaill (often known in English as Finn MacCool) has had a long life. First cited in Old Irish chronicles from the early Christian era, he became the central hero of the Fenian Cycle which flourished in the high Middle Ages. Stories about Fionn and his warriors continue to be told by storytellers in Ireland and in Gaelic Scotland to this day.

This book traces the development of Fionn's persona in Irish and Scottish texts and constructs a heroic biography of him. As aspects of the hero are borrowed into English and later world literature, his personality undergoes several changes. Seen as less than admirable, he may become either a buffoon or a blackguard. Somehow these contradictions exist side by side.

Among the writers in English most interested in Fionn are James Macpherson, the "translator" of The Poems of Ossian ( 17601, William Carleton, the first great fiction writer of nineteenth-century Ireland, and Fiann O'Brien, the multifaceted author of At Swim-Two-Birds. Aspects of Fiann appear as far apart as Mendelssohn's "Hebrides (or Fingal 's Cave) Overture" and a contemporary rock opera. But the most complex use of Fionn's story in modern
literature is James Joyce's Finnegans Wake.