The Fenian Brotherhood 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. Members were commonly known as "Fenians". O'Mahony, who was a Celtic scholar, named his organisation after the Fianna, the legendary band of Irish warriors led by Fionn mac Cumhaill.