Sir Robert David Muldoon GCMG CH PC (/mʌlˈduːn/; 25 September 1921 – 5 August 1992) was a New Zealand politician who served as the 31st prime minister of New Zealand, from 1975 to 1984, while leader of the National Party. Departing from National Party convention, Muldoon was a right-wing populist and economic nationalist, with a distinctive public persona described as reactionary, aggressive, and abrasive.

After a troubled childhood, Muldoon served as a corporal and sergeant in the army in the Second World War. After a career as a cost accountant, he was elected to the House of Representatives at the 1960 general election as the Member of Parliament (MP) for Tamaki, representing the National Party. Muldoon rose in the Second National Government to serve successively as Minister of Tourism (1967), Minister of Finance (1967–1972), and Deputy Prime Minister (1972). Over this time he built up an informal but solid backing amongst National's mostly rural right faction, which he called "Rob's Mob". After National lost the 1972 general election to the Labour Party, Muldoon used his connections to oust moderate party leader Jack Marshall and take his place, becoming Leader of the Opposition in 1974. Through Muldoon's ideological blend of moderate social liberalism and protectionist right-wing populism ("counterpunching", a term he coined) and the promise of a lucrative superannuation scheme, National enjoyed a resurgence. The early death of prime minister Norman Kirk severely weakened the Labour Party, and Muldoon soon led National to a decisive victory in the 1975 general election.

Muldoon came to power promising to lead "a Government of the ordinary bloke". He appointed himself Minister of Finance. Although he used populist rhetoric to rail against elites and the political establishment, he consistently tried to centralise power under himself during his premiership. His tenure was plagued by an economic pattern of stagnation, high inflation, growing unemployment, and high external debts and borrowing. Economic policies of the Muldoon Government included national superannuation, wage and price freezes, industrial incentives, and the Think Big industrial projects. He reintroduced and intensified the previous government's policies of the Dawn Raids, which racially targeted Pasifika overstayers. To engage with crime, Muldoon built "unusually close relationships" with criminal gangs; he personally favoured Black Power, and he and his wife Thea met with them on several occasions. In foreign policy, Muldoon adopted an anti-Soviet stance and re-emphasised New Zealand's defence commitments to the United States and Australia under the ANZUS pact. His refusal to stop a Springbok rugby tour of New Zealand divided the country and led to unprecedented civil disorder in 1981. Muldoon became more and more controversial as his premiership progressed; in addition to the controversy of the Springbok tour, he began a smear campaign against Labour MP Colin Moyle for alleged illegal homosexual activities and punched demonstrators at a protest.

Muldoon led his party to two additional election victories in 1978 and 1981, with the first-past-the-post electoral system keeping him in power despite losing the popular vote in each election except 1975. At the 1984 snap election, which Muldoon infamously announced while intoxicated on live television, National finally suffered a significant defeat to Labour. Shortly before leaving office, amid a constitutional crisis, Muldoon was forced by the incoming Government to devalue the New Zealand dollar. In 1984, he was only the second prime minister (after Sir Keith Holyoake) to receive a knighthood while still in office. Mounting legal costs encouraged Muldoon to pursue a novelty acting career, but he remained in parliament until his retirement in 1992. He died shortly thereafter; the gang Black Power performed a haka at his funeral.

Robert David Muldoon was born in Auckland on 25 September 1921 to parents James Henry Muldoon and Amie Rusha Muldoon (née Browne). His father's family, the Muldoon (Irish: Ó Maoldúin) family, were of Irish descent; his grandfather was an Irish-born Scouser who emigrated from Liverpool.

At the age of five, 'Rob' Muldoon slipped while playing on the front gate, damaging his cheek and resulting in a distinctive lopsided smile that remained with him for life.

When Muldoon was aged eight, his father was admitted to Auckland Mental Hospital at Point Chevalier, where he died of parenchymatous syphilis nearly 20 years later in 1946. This left Muldoon's mother to raise him on her own. During this time Muldoon came under the strong formative influence of his fiercely intelligent, iron-willed maternal grandmother Jerusha, a committed socialist. Though Muldoon never accepted her creed, he did develop under her influence a potent ambition, a consuming interest in politics, and an abiding respect for New Zealand's welfare state. Muldoon won a scholarship to attend Mount Albert Grammar School from 1933 to 1936. He left school at age 15, finding work at Fletcher Construction and then the Auckland Electric Power Board as an arrears clerk. He studied accountancy by correspondence.

In 1951 Muldoon married Thea Dale Flyger, who he had met through the Junior Nationals. The couple had three children. Lady Muldoon, who died at age 87 in 2015, was appointed a Dame Commander of the Order of the British Empire in the 1993 New Year Honours and made a Companion of the Queen's Service Order in the 1986 New Year Honours. Muldoon was protective of his family life and, in particular, his wife. He said that people could comment about him but his family was off limits.