Irish nationalist military leader and popular conservative head of the United Ireland Party who played a significant role in the development of the Irish armed forces and police. His support of fascism in the 1930s, however, cost him much of his public support.

Joining the Irish rebels against England in 1917, O'Duffy became commander of the Irish Army (1924–25) after the formation of the Irish Free State (1921) and served as chief commissioner of the Civic Guard (police) from 1922 to 1933. After his removal in 1933 he joined the opposition to Pres. Eamon de Valera and helped found the anti-Communist United Ireland Party, serving as its president from 1933 until his forced resignation the next year. Head of the Fascist Blue Shirts (Blue Shirt) from 1933, he lost most of his remaining prestige in an abortive effort to aid Franco during the Spanish Civil War (1936–39) and died disgraced.