Alexander Boris de Pfeffel Johnson (; born 19 June 1964) is a British politician, writer, and former journalist serving as Prime Minister of the United Kingdom and Leader of the Conservative Party since July 2019. He has been Member of Parliament (MP) for Uxbridge and South Ruislip since 2015 and was MP for Henley from 2001 to 2008. He also served as Mayor of London from 2008 to 2016 and Foreign Secretary from 2016 to 2018. Johnson identifies as a one-nation conservative.

Born in New York City to upper-middle class British parents, Johnson was educated at the European School, Brussels I, Ashdown House, and Eton College. He read Classics at Balliol College, Oxford, where he was elected President of the Oxford Union in 1986. He began his career in journalism at The Times but was dismissed for falsifying a quotation. He became The Daily Telegraph's Brussels correspondent, and his articles exerted a strong influence on growing Eurosceptic sentiment on the British right. He was an assistant editor of The Telegraph from 1994 to 1999, and edited The Spectator from 1999 to 2005. He was elected MP for Henley in 2001, and served as a Junior Shadow Minister under Conservative leaders Michael Howard and David Cameron. He largely adhered to the Conservatives' party line but adopted a socially liberal stance on issues such as LGBT rights in parliamentary votes. Resigning as an MP, in 2008 he was elected Mayor of London, and was re-elected in 2012. During his mayoralty, he banned alcohol consumption on much of London's public transport, oversaw the 2012 Summer Olympics, and introduced the New Routemaster buses, cycle hire scheme, and Thames cable car.

In 2015, Johnson was elected MP for Uxbridge and South Ruislip, stepping down as Mayor the following year. In 2016, he became a prominent figure in the successful Vote Leave campaign for Brexit. He then served as Secretary of State for Foreign and Commonwealth Affairs under Theresa May's premiership - a post from which he resigned in criticism of May's approach to Brexit and the Chequers Agreement two years later. After May resigned in 2019, he was elected Conservative leader and appointed prime minister. In August 2019, Johnson controversially advised Queen Elizabeth II to prorogue Parliament from 10 September to 14 October; on 24 September this action was unanimously ruled to be unlawful and of no effect by the Supreme Court. In September 2019, Johnson suspended 21 of his own Conservative MPs.

Johnson is a controversial figure in British politics and journalism. Supporters have praised him as an entertaining, humorous, and popular figure, with an appeal stretching beyond traditional Conservative voters. He has been accused of dishonesty, elitism, and cronyism, and of using racist, sexist, and homophobic language. Johnson is the subject of several biographies and a number of fictionalised portrayals.