London — British Prime Minister Theresa May is set to step down Wednesday and be replaced by former London mayor and U.K. foreign minister Boris Johnson. President Donald Trump has said he thinks Johnson, who is known domestically for an off-beat brand of charisma, political opportunism, and promoting a hard break from the European Union, will do a "great job" as prime minister.

Johnson began his career as a journalist. After being fired from one paper for making up a quote, he was sent to Brussels to work for another newspaper, The Telegraph, where he published a number of stories that were reportedly either exaggerated or untrue. When he returned to London, he became an editor at the conservative magazine The Spectator.

He was elected to Parliament in 2001. As a Member of Parliament (MP), Johnson was involved in a controversy relating to a years-long extramarital affair with a colleague at The Spectator. He was removed from a senior role within his Conservative Party for falsely denying the reports.

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A year later, however, he was promoted to another high-profile role within his party. He eventually resigned from The Spectator, but continued writing sometimes-controversial columns for The Telegraph, at one point having to apologize to the country of Papua New Guinea for linking it to "cannibalism and chief-killing."

Boris Johnson Getty

Johnson then served as the mayor of London from 2008 to 2016, promoting some infamously expensive projects, including a "garden bridge" across the river Thames that cost £50 million, despite never being constructed.

His reputation was bolstered by London's successful hosting of the 2012 Summer Olympics.

In 2015, Johnson said then-Republican presidential candidate Donald Trump betrayed "a quite stupefying ignorance" for saying there were "no-go" areas for police in Paris and London because of high Muslim populations. Johnson said Mr. Trump was "unfit to hold the office of President of the United States."

Johnson won a seat again as an MP in 2015 in the lead-up to the Brexit referendum, and, despite having spoken favorably about Britain's place in the EU single market during his time as London mayor, he campaigned hard for the U.K. to leave the European Union. The apparent switch saw him criticized by some for political opportunism.

After the surprise results of the Brexit referendum, in which Britain voted to leave the EU by 52% to 48%, Johnson was appointed foreign secretary by the country's new prime minister, Theresa May.

He resigned from that role in 2018 in protest of May's Brexit deal, which was negotiated over the course of two years with EU officials in Brussels. He and other hard-line "Brexiteers" said the draft agreement was a betrayal of the public will and would leave the U.K. too closely tied to the European Union.

Johnson has remained supportive of a hard Brexit, saying Britain should leave the EU by Oct. 31 this year, even if no deal has been reached for future relations with the European Union.

"I say to all the doubters: Dude, we are going to energize the country, we are going to get Brexit done," Johnson said Tuesday.