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Harold Holt was an Australian politician who served as the 21st Prime Minister of Australia from 1966 until his disappearance at sea in 1967. Holt was a member of the Liberal Party and served as Minister for Immigration from 1949 to 1956, Minister for Defence from 1956 to 1961, and Treasurer from 1961 to 1966. He succeeded Robert Menzies as Prime Minister in 1966.