Ong Iok-tek (Ikutoku Ō; /; POJ: Ông Io̍k-tek; Hepburn:Ō Ikutoku: ; 30 January 1924–9 September 1985) was a Taiwanese scholar and early leader of the Taiwan independence movement. He is considered to be an authority on the Southern Min language family and the Taiwanese language.
He was born in Tainan Prefecture (modern-day Tainan), during Japanese rule, of a prominent family. He attended Tokyo Imperial University in 1943 but the ongoing World War II compelled him to return to Taiwan after a year. Following the war and handover of Taiwan he took a critical attitude toward the Kuomintang, one accentuated by the killing of his brother, , a Tokyo-educated prosecutor, in the February 28 Incident. His own life threatened by the new regime, he fled to Japan in 1949 and spent the rest of his life there in addition to various other places.
He resumed his studies in May 1950, and after completing his Ph.D. in 1969 at the University of Tokyo,