Spencer Perceval (1 November 1762 11 May 1812) was a British statesman and barrister who served as Prime Minister of the United Kingdom from October 1809 until his assassination in May 1812. Perceval is the only British prime minister to have been assassinated, and the only solicitor-general or attorney-general to have become prime minister.

The younger son of an Anglo-Irish earl, Perceval was educated at Harrow School and Trinity College, Cambridge. He studied law at Lincoln's Inn, practised as a barrister on the Midland circuit, and in 1796 became a King's Counsel. He entered politics at age 33 as a member of Parliament (MP) for Northampton. A follower of William Pitt the Younger, Perceval always described himself as a "friend of Mr. Pitt", rather than a Tory. Perceval was opposed to Catholic emancipation and reform of Parliament; he supported the war against Napoleon and the abolition of the Atlantic slave trade. He was opposed to hunting, gambling and adultery; he did not drink as much as most MPs at the time, gave generously to charity, and enjoyed spending time with his thirteen children.

After a late entry into politics, his rise to power was rapid: he was appointed as Solicitor General and then Attorney General for England and Wales in the Addington ministry, Chancellor of the Exchequer and Leader of the House of Commons in the second Portland ministry, and then became prime minister in 1809. At the head of a weak government, Perceval faced a number of crises during his term in office, including an inquiry into the Walcheren expedition, the madness of King George III, economic depression, and Luddite riots. He overcame those crises, successfully pursued the Peninsular War in the face of opposition defeatism, and won the support of the Prince Regent. His position was looking stronger by early 1812, when, in the lobby of the House of Commons, he was assassinated by a merchant with a grievance against his government.

Perceval had four older brothers who survived to adulthood. Through expiry of their male-line, male heirs, the earldom of Egmont passed to one of his great-grandsons in the early twentieth century and became extinct in 2011.

The prime minister of the United Kingdom is the head of government in the United Kingdom. The prime minister advises the sovereign on the exercise of much of the royal prerogative, chairs the Cabinet and selects its ministers. As modern prime ministers hold office by virtue of their ability to command the confidence of the House of Commons, they sit as a member of Parliament.

The office of prime minister is not established by any statute or constitutional document, but exists only by long-established convention, whereby the reigning monarch appoints as prime minister the person most likely to command the confidence of the House of Commons; this individual is typically the leader of the political party or coalition of parties that holds the largest number of seats in that chamber. It was announced by Prime Minister Boris Johnson on 31 January 2022 that the office of Prime Minister would be formally established.The prime minister is ex officio also First Lord of the Treasury, Minister for the Civil Service and the minister responsible for national security.: p.22  Indeed, certain privileges, such as residency of 10 Downing Street, are accorded to prime ministers by virtue of their position as First Lord of the Treasury. In 2019, the office of Minister for the Union was established; Boris Johnson became the first prime minister to hold this title.