When asked in 2007 to defend his combative, abrasive and confrontational approach while serving three US presidents, John Bolton pointed to his first job, rather than anything in government.
"I am a lawyer," he told The New York Times. On Monday, he will start work with a fourth occupant of the White House: Donald Trump.
Mr Bolton's appointment, as the president's national security adviser, has been dominated by questions about past judgments, as much as curiosity over decisions to come.
To his allies, Mr Bolton is a zealous, principled lightning rod for championing a US centric — at times military driven — agenda abroad. As undersecretary for Arms Control (2001-2005), he was important in the Proliferation Security Initiative, a global effort aimed at interdicting and blocking trafficking of weapons of mass destruction.
He also helped in his short and controversial term as ambassador to the United Nations (2005-2006) bring to the floor non-proliferation resolutions to pressure North Korea and Iran on their nuclear programmes. But at the UN he also showed disregard for diplomacy at a time when the Iraq war was spiralling toward a sectarian bloodbath.
To his critics, Mr Bolton epitomises disruption, unilateralism and a bullying personal character in pursuing and executing policy.
Replacing General HR McMaster, Mr Bolton's new position is "arguably the most influential in US national security and foreign policy" Phil Gordon, a former White House and State Department official in the Obama administration told The National.
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The job gives him access to the Oval Office that is "closer than the Secretaries of State and Defence", Mr Gordon said.
That could lead to unparalleled influence.
"Normally, the primary responsibility for the NSA is to be an honest broker within the national security staff but John Bolton is not known to be a fair broker," Mr Gordon said, anticipating that the new NSA chief will use the job to push his own views and agenda.
To say that Mr Bolton has strong views on foreign policy would be an understatement. He famously said "there is no United Nations", and that "we are confident that Saddam Hussein has hidden weapons of mass destruction".
He has advocated regime change in Iran and North Korea, was accused of spinning US intelligence on Cuba, was a big backer of the Iraq war, proposed a three state solution for Israel and the Palestinians, and called for a Sunni state in Syria.
"Mr Bolton is someone who is prepared to go to war, and has shown an absolute hostility to diplomacy, a disdain for co-operation with partners and for international organisations," said Mr Gordon.
In 2002 Mr Bolton described America's withdrawal of the International Criminal Court as "the happiest moment" of his career, and he led negotiations to withdraw from the anti-ballistic missile treaty.
Elliott Abrams, a former White House official who worked with Mr Bolton in the George W Bush presidency, described the new NSA as one of the "strongest and brightest" picks for the job.
Mr Bolton also served presidents Ronald Reagan and George H W Bush.
Mr Trump was close to nominating Mr Bolton in November of 2016. The recent change of heart is not surprising to Mr Abrams.
"He has been on the president’s mind and they have been meeting regularly," he said.
"John's strongest attribute is making sure the president's policy is implemented through the vast federal US bureaucracy."
White House Chief of Staff John Kelly reportedly tried to block the meetings, only to find himself sidelined before the exit of Mr McMaster last month.
Two conservative political figures in Washington who did not wish to be named, described Mr Bolton as a relentless, stubborn and argumentative figure.
"You don’t want to get on his bad side," one said.
A Republican who works on foreign policy in Washington told The National on condition of anonymity said Mr Bolton was "very bright and a principled adherent to a set of ideas but he is neither flexible nor a team player".
During his tenure at the State Department between 2001 and 2005 Mr Bolton often clashed with his boss Colin Powell and worked the tools of bureaucracy to undermine anyone who opposed him.
This could put him at odds with Secretary of Defence James Mattis, who according to the Washington Post had refused in the last year to hand the White House military options to strike Iranian ballistic missile factories.
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In his own words: John Bolton's views on world issues
Trump appoints Bolton as US national security adviser
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In the Middle East, Mr Bolton's biggest impact could be on Iran. He has frequently lambasted the Islamic Republic and with a May 12 deadline looming on US negotiations with European partners, Russia and China to amend the Iran nuclear deal, both Mr Bolton’s allies and critics agree that his appointment makes it more likely that Washington will abandon the agreement.
Mr Bolton's credibility could be coloured by his connections to the Mujahedin-e Khalq (MEK), a group formally designated as terrorists by the State Department in 1997 having ran a bombing campaign inside Iran, including against American organisations such as Pepsi Cola and General Motors, during the US-backed reign of the Shah in the 1970s.
The US terrorist designation was lifted in 2012, after the group said it had renounced violence and following a concerted lobbying campaign in Congress and among former US government officials.
Mr Bolton addressed a MEK event in Paris last year, and openly called for regime change in Tehran.
His opponents often call him a neoconservative, but his foreign policy views appear to be closer to former vice president Dick Cheney and former Secretary of State James Baker than to noted neocons such as Paul Wolfowitz.
Mr Bolton is not an advocate for democracy and human rights abroad, but "sees policy through the lens of power and influence", said Adam Ereli, a former US ambassador to Bahrain who worked with Mr Bolton at the State Department.
Other controversies include Mr Bolton reportedly threatening Jose Boustani, a retired Brazilian diplomat and former head of the Organisation for the Prohibition of Chemical Weapons, in 2002.
Mr Bolton's Achilles heel could be Mr Trump himself. While both men are known for their combative approaches, and fondness for media attention, Mr Bolton's fixed views could clash with the president's unpredictable approach to government, as well as apparent willingness to pursue an isolationist foreign policy.
