Sir John Ross Marshall (5 March 1912 – 30 August 1988), generally known as Jack Marshall, was a New Zealand politician of the National Party. After spending twelve years as Deputy Prime Minister, he served as the 28th Prime Minister for most of 1972. The Third National Government, in office since 1960, appeared worn-out and out of touch, and at the time of Marshall's appointment as Prime Minister seemed headed for heavy electoral defeat. After Labour's victory in the 1972 election, Marshall became Leader of the Opposition. He was determined to remain as leader of the National Party, but in July 1974 was challenged for the leadership by Robert Muldoon, his deputy, rival and successor.