Winston Churchill, a Conservative leader was the first PM in Queen Elizabeth's reign.
Liz Truss, who won the Conservative party leadership election on Monday, was the 15th and the last UK Prime Minister during the reign of head of state Queen Elizabeth II who died on Thursday.
Here is a list of the previous occupants of 10 Downing Street since the queen came to the throne in 1952.
Winston Churchill (Conservative, 1951-55)
Anthony Eden (Conservative, 1955-57)
Harold Macmillan (Conservative, 1957-63)
Alec Douglas-Home (Conservative, 1963-64)
Harold Wilson (Labour, 1964-70)
Edward Heath (Conservative, 1970-74)
Harold Wilson (Labour, 1974-76)
James Callaghan (Labour, 1976-79)
Margaret Thatcher (Conservative, 1979-90)
John Major (Conservative, 1990-97)
Tony Blair (Labour, 1997-2007)
Gordon Brown (Labour, 2007-10)
David Cameron (Conservative, 2010-16)
Theresa May (Conservative, 2016-19)
Boris Johnson (Conservative, 2019-22)