David Lloyd George, 1st Earl Lloyd-George of Dwyfor, (17 January 1863 – 26 March 1945) was Prime Minister of the United Kingdom from 1916 to 1922. A Liberal Party politician from Wales, he was known for leading the United Kingdom during the First World War, for social-reform policies (including the National Insurance Act 1911), for his role in the Paris Peace Conference, and for negotiating the establishment of the Irish Free State. He was the last Liberal Party prime minister; the party fell into third-party status shortly after the end of his premiership.

After becoming active in local politics, Lloyd George gained a reputation as an orator and a proponent of a Welsh blend of radical Liberalism, that included support for Welsh devolution, for the disestablishment of the Church of England in Wales, for equality for labourers and tenant farmers, and for reform of land ownership. In 1890, he narrowly won a by-election to become the Member of Parliament for Caernarvon Boroughs, in which seat he remained for 55 years. He served in Henry Campbell-Bannerman's cabinet from 1905. After H. H. Asquith succeeded to the premiership in 1908, Lloyd George replaced him as Chancellor of the Exchequer. To fund extensive welfare reforms he proposed taxes on land ownership and high incomes in the "People's Budget" (1909), which the Conservative-dominated House of Lords rejected. The resulting constitutional crisis was only resolved after two elections in 1910 and the passage of the 1911 Parliament Act. His budget was enacted in 1910, and the National Insurance Act 1911 and other measures helped to establish the modern welfare state. In 1913, he was embroiled in the Marconi scandal, but he remained in office and promoted the disestablishment of the Church of England in Wales until 1914, when its implementation was suspended in response to the outbreak of the First World War.

As wartime chancellor, Lloyd George strengthened the country's finances and forged agreements with trade unions to maintain production. In 1915, Asquith formed a Liberal-led wartime coalition with the Conservatives and Labour. Lloyd George became Minister of Munitions and rapidly expanded production. Amongst other measures, he set up four large munitions factories as a countermeasure to the shell crisis of the previous year. The so-called 'National Filling Factory' in Renfrewshire was named 'Georgetown' in Lloyd George's honour. In 1916, he was appointed Secretary of State for War but was frustrated by his limited power and by clashes with the military establishment over strategy. Amid stalemate on the Western Front, confidence in Asquith's leadership as prime minister waned, and he resigned in December 1916. Lloyd George succeeded him as prime minister, supported by the Conservatives and some Liberals. He centralised authority by creating a smaller war cabinet, a new Cabinet Office and what he called his "Garden Suburb" of advisers. To combat food shortages he implemented the convoy system, established rationing, and stimulated farming. After supporting the disastrous French Nivelle Offensive in 1917, he had to reluctantly approve Field Marshal Haig's plans for the Battle of Passchendaele, which again resulted in huge casualties with little strategic benefit. Against the views of British military commanders, he was finally able to see the Allies brought under one command in March 1918. The war effort turned in their favour in August and was won in November. In the aftermath, and following the December 1918 "Coupon" election, he and the Conservatives maintained their coalition with popular support. Earlier that year his government had extended the franchise to all men and some women.

Lloyd George was a major player in the Paris Peace Conference of 1919, but the situation in Ireland worsened that year, erupting into the Irish War of Independence, which lasted until Lloyd George negotiated independence from the UK for the Irish Free State in 1921. At home, he initiated reforms to education and housing, but trade-union militancy rose to record levels, the economy became depressed in 1920 and unemployment rose; spending cuts followed in 1921–22, and in 1922 he became embroiled in a scandal over the sale of honours and the Chanak Crisis. The Carlton Club meeting resulted in backbench support for the Conservatives to end the coalition and to contest the next election alone. Lloyd George resigned as prime minister and never held office again, but continued as the leader of a Liberal faction. After an awkward reunion with Asquith's faction in 1923, Lloyd George led the Liberals from 1926 to 1931. He put forward innovative proposals for public works and other reforms in a series of coloured books, but made only modest gains in the 1929 election. After 1931, he was a mistrusted figure heading a small rump of breakaway Liberals who were opposed to the National Government. In 1940, he refused to serve in Winston Churchill's War Cabinet. He was elevated to the peerage in 1945, shortly before his death.