William Ewart Gladstone ( GLAD-stən; 29 December 1809 – 19 May 1898) was a British statesman and Liberal politician. In a career lasting over 60 years, he served for 12 years as Prime Minister of the United Kingdom, spread over four non-consecutive terms (the most of any British prime minister) beginning in 1868 and ending in 1894. He also served as Chancellor of the Exchequer four times, for over 12 years.

Gladstone was born in Liverpool to Scottish parents. He first entered the House of Commons in 1832, beginning his political career as a High Tory, a grouping that became the Conservative Party under Robert Peel in 1834. Gladstone served as a minister in both of Peel's governments, and in 1846 joined the breakaway Peelite faction, which eventually merged into the new Liberal Party in 1859. He was chancellor under Lord Aberdeen (1852–1855), Lord Palmerston (1859–1865) and Lord Russell (1865–1866). Gladstone's own political doctrine—which emphasised equality of opportunity and opposition to trade protectionism—came to be known as Gladstonian liberalism. His popularity amongst the working-class earned him the sobriquet "The People's William".

In 1868, Gladstone became prime minister for the first time. Many reforms were passed during his first ministry, including the disestablishment of the Church of Ireland and the introduction of secret voting. After electoral defeat in 1874, Gladstone resigned as leader of the Liberal Party. From 1876 he began a comeback based on opposition to the Ottoman Empire's reaction to the Bulgarian April Uprising. His Midlothian Campaign of 1879–1880 was an early example of many modern political campaigning techniques. After the 1880 general election, Gladstone formed his second ministry (1880–1885), which saw the passage of the Third Reform Act as well as crises in Egypt (culminating in the Fall of Khartoum) and Ireland, where his government passed repressive measures but also improved the legal rights of Irish tenant farmers.

Back in office in early 1886, Gladstone proposed home rule for Ireland but was defeated in the House of Commons. The resulting split in the Liberal Party helped keep them out of office—with one short break—for 20 years. Gladstone formed his last government in 1892, at the age of 82. The Government of Ireland Bill 1893 passed through the Commons but was defeated in the House of Lords in 1893, after which Irish Home Rule became a lesser part of his party's agenda. Gladstone left office in March 1894, aged 84, as both the oldest person to serve as Prime Minister and the only prime minister to have served four non-consecutive terms. He left Parliament in 1895 and died three years later.

Gladstone was known affectionately by his supporters as "The People's William" or the "G.O.M." ("Grand Old Man", or, to political rivals "God's Only Mistake"). Historians often rank Gladstone as one of the greatest prime ministers in British history.