Casey, from the Irish O’Cathasaigh, is a common surname in Ireland originally meaning “vigilant” or “watchful.” John Keegan “Leo” Casey (1846 – 1870) was a poet, novelist and orator as well as a famous Republican in the Fenian Rising. At the age of fifteen he wrote the famous song The Rising of the Moon to commemorate the Irish Rebellion of 1798. Another famous O’Casey writer was 20th century playwright Seán O’Casey (1880-1964), pictured above. Born John Casey, Seán adopted the Gaelic spelling of his name as his interest in the Irish nationalist cause grew.