Britain's Prime Minister Boris Johnson returns to 10 Downing Street after meeting with Queen Elizabeth II at Buckingham Palace, London, on Friday, Dec. 13, 2019.

Video. From dizzying heights to tumultuous lows, the UK's Boris Johnson quits

He was the mayor who reveled in the glory of hosting the 2012 London Olympics, and the man who led the Conservatives to a whopping election victory on the back of his mission to “get Brexit done.”