As of 2017, who is the only British Prime Minister to serve under three monarchs?

Stanley Baldwin, 1st Earl Baldwin of Bewdley, KG, PC, JP, FRS (3 August 1867 – 14 December 1947) was a British Conservative politician who dominated the government in his country between the two world wars. Three times Prime Minister, he is the only premier to have served under three monarchs (George V, Edward VIII and George VI).

Baldwin first entered the House of Commons in 1908 as the Member of Parliament for Bewdley, in succession to his father Alfred Baldwin. He held government office in the coalition ministry of David Lloyd George. In 1922, Baldwin was one of the prime movers in the withdrawal of Conservative support from Lloyd George; he subsequently became Chancellor of the Exchequer in Bonar Law's Conservative ministry. Upon Bonar Law's resignation due to health reasons in May 1923, Baldwin became Prime Minister and Conservative Party leader. He called an election on the issue of tariffs and lost the Conservatives' majority, after which Ramsay MacDonald formed a minority Labour government.