William Massey, Irish-New Zealand farmer and politician, 19th Prime Minister of New Zealand (d. 1925)
William Ferguson Massey (26 March 1856 – 10 May 1925), commonly known as Bill Massey, was a politician who served as the 19th prime minister of New Zealand from May 1912 to May 1925. He was the founding leader of the Reform Party, New Zealand's second organised political party, from 1909 until his death.

Massey was born in County Londonderry in Ireland (now Northern Ireland). After migrating to New Zealand in 1870, Massey farmed near Auckland (earning his later nickname, Farmer Bill) and assumed leadership in farmers' organisations. He entered parliament in 1894 as a conservative, and from 1894 to 1912 was a leader of the conservative opposition to the Liberal ministries of Richard Seddon and Joseph Ward. Massey became the first Reform Party Prime Minister after he led a successful motion of no confidence against the Liberal government. Throughout his political career Massey was known for the particular support he showed for agrarian interests, as well as his opposition to organised labour. He pledged New Zealand's support for Britain during the First World War.

Massey led his Reform Party through four elections, although only the 1919 election was a decisive victory over all other parties. Following increasingly poor health in his fourth term, Massey died in office. After Richard Seddon, he is the second-longest-serving Prime Minister of New Zealand.