Sultan Ismail Nasiruddin Shah ibni Almarhum Sultan Zainal Abidin III KCMG was the fourth Yang di-Pertuan Agong of Malaysia (roughly equivalent to King), and the fifteenth Sultan of Terengganu.
The date of his birth has been given as either 16 March 1906 or as 24 January 1907, the latter being the one more often used. Born in Kuala Terengganu, he was the fifth, but third surviving, son of Sultan Zainal Abidin III ibni Almarhum Sultan Ahmad II. His mother was a Thai Muslim convert, Cik Maimuna binti Abdullah, who died in 1918.
When the British returned after the end of World War II, they declined to recognise the previous Sultan Ali Shah. Allegedly, Sultan Ali was too much in debt and had been too close to the Japanese during their occupation. According to Sultan Ali, the British Military Administration wanted him removed for his refusal to sign the Malayan Union treaty. On 5 November 1945 the Terengganu State Council of thirteen members announced the dismissal of Sultan Ali and the appointment of Tengku Ismail as the fifteenth Sultan of Terengganu. Tengku Ismail became known as Sultan Ismail Nasiruddin Shah and was installed on 6 June 1949 at Istana Maziah, Kuala Terengganu.
Sultan Ismail was elected the fourth Yang di-Pertuan Agong of Malaysia and served in that office from 21 September 1965 until 20 September 1970.