Born: 1816, County
Died: February 7, 1877, New York
Originally a member of the Young Ireland movement, John O'Mahony took charge of the American wing of the Fenian Brotherhood. He also organized the Fenian regiment during the American Civil War. After the failed attack on Canada (an attempt to force the British into giving Ireland its freedom by holding Canada hostage), O'Mahony stepped down from some of his leadership roles though he continued living in New York. O'Mahony was a journalist and writer as well, one of his books being The History of Ireland, published in 1857.
For more on John O'Mahony, please see http://concise.britannica.com/ebc/article?eu=399325.