Eoin O'Duffy (Irish: Eoin Ó Dubhthaigh; born Owen Duffy, 28 January 1890 – 30 November 1944) was a prominent Irish nationalist. He was commander of the Irish army (1924–25) and chief commissioner of the police (1922–1933). Later in life, he was influenced by anti-Communism, corporatism, and fascism (broad sense).
In 1933, he became the leader of the Army Comrades Association ("the Blueshirts"). After the merger of various pro-Treaty factions under the banner of Fine Gael, O'Duffy was the party leader for a short time (1933–1934). In 1935, he launched the National Corporate Party, with "the Greenshirts" as a paramilitary wing (1935–1937). O'Duffy left Ireland in 1936 to lead the volunteer Irish Brigade (Spanish Civil War) in the Spanish Civil War. He retired on his return in 1937 and wrote a book, Crusade in Spain (1938), about the Irish Brigade in Spain. He had some contacts with National Socialist Germany during WWII.
O'Duffy made an appearance at the 1934 International Fascist conference in Montreux where he argued against anti-Semitism, telling the conference that they had "no Jewish problem in Ireland". On the other hand, the later Crusade In Spain is stated to have had anti-Semitic undertones.