U.S. President Donald Trump's choice of John Bolton to replace Army Lieutenant General H.R. McMaster as national security advisor replaces a restraining influence in the president's inner circle with a dedicated hawk.
Bolton is known as a colorful figure in Washington and an inveterate bureaucratic infighter. On his desk at the State Department during the administration of former Republican President George W. Bush, he kept a defused hand grenade.
In 2003, on the eve of six-nation talks over Pyongyang's nuclear program, he lambasted then North Korean leader Kim Jong Il in a speech in Seoul, calling him a "tyrannical dictator."
North Korea responded by calling Bolton "human scum."
Like Trump, Bolton did not serve in the Vietnam War, instead joining the Army National Guard.
Bolton's sometimes abrasive style got him into trouble in the Bush administration. One incident that came back to haunt him was his reported dressing-down of an intelligence analyst who questioned him over whether Cuba had an advanced chemical and biological weapons program.
During his 2005 confirmation hearing to become U.N. ambassador, State Department intelligence chief Carl Ford called Bolton "a serial abuser" and "a quintessential kiss-up, kick-down sort of guy."
The Senate never approved Bolton's nomination. Bush instead appointed him to the U.N. post for 17 months under a process known as a recess appointment that bypasses confirmation.
In a Fox News interview on Thursday evening, after news of his appointment broke, Bolton appeared to temper his often harsh rhetoric. "Frankly, what I have said in private now, is behind me, at least effective April 9," he said, referring to the date he is scheduled to take over from McMaster.
The White House national security adviser post does not require Senate confirmation. In that job, Bolton will oversee a White House national security staff of several hundred specialists, many on loan from the Pentagon, State Department and U.S. intelligence agencies.
He will be responsible for advising Trump on a dizzying array of issues, from the fight against Islamic State and al Qaeda to China's expanding economic and military power.
In Seoul, conservative lawmaker Kim Hack-yong expressed concern about Bolton's appointment in advance of a planned summit between Trump and North Korean leader Kim Jong Un.
"This is worrisome news. North Korea and the United States need to have dialogue, but this only fuels worries over whether the talks will ever happen," Kim said. "If Bolton takes office and talks with North Korea go haywire and yield bad results, I don't know what we'll do then."
Mark Dubowitz, chief executive of the Foundation for Defense of Democracies think tank, who advises the White House on Iran policy, said Bolton would support abrogating the Iran nuclear deal if Britain, France and Germany fail to meet Trump's demand for new limits on Tehran's program by mid-May.
"My long-standing support for a fix for the Iran deal may have just died an untimely death," said Dubowitz, who backs preserving the deal by closing what he argues are fatal loopholes in the pact.
Bolton has applauded Trump's plan to move the U.S. embassy in Israel to Jerusalem, advocated keeping the Guantanamo Bay prison in Cuba open, and proposed increasing pressure on China by boosting U.S. support to Taiwan, which Beijing considers a renegade province.
Judging by his Twitter feed, Bolton is more hawkish on Russia than his new boss, Trump.
While dismissing allegations that Trump's campaign colluded with the Kremlin, Bolton has been outspoken about alleged Russian meddling in the 2016 U.S. presidential election.
When Russian President Vladimir Putin announced new nuclear weapons on March 1, Bolton responded with trademark bellicosity.
"There needs to be a strategic response to Russia's new nuclear missiles to show our allies in Europe that we will not let #Russia push the U.S. or its allies around," he wrote.