Eugen Dido Kvaternik (29 March 1910 – 10 March 1962) was a Croatian Ustaše General-Lieutenant and the Chief of the Internal Security Service in the Independent State of Croatia, a Nazi puppet state during World War II.
Eugen Dido Kvaternik was son of Slavko Kvaternik, a general in the Independent State of Croatia army and a member of the Ustaše, and Olga Frank, daughter of Josip Frank, a Catholic convert whose parents were Jewish.
He instituted a regime of terror against Croatian Serbs, Jews, Gypsies and other "enemies of the State". In 1943, after a falling-out with Pavelić, the leader of the Independent State of Croatia, he and his father, Slavko, the Croatian Minister of War, went into exile in Slovakia, and after the war fled to Argentina with the assistance of Roman Catholic clerics and their ratlines. From Argentina, he directed activities against Josip Broz Tito. He reorganized Ustaše supporters and continued to publish actively. Yugoslavia's multiple extradition requests were all turned down, and Kvaternik was never tried. Dido Kvaternik died in a car crash in Río Cuarto, Argentina in 1962.
Kvaternik met Marija Cvitković in 1941; the two married on 10 January 1942. The couple had three children: Slavko, Davor and Olga. Slavko later became a professor of political sciences in Argentina, and Davor became a cardiologist in Boston, Massachusetts. Olga died with her father in the same car accident on 10 March 1962. He was survived by his widow, Marija, and their two sons.