John Bolton is a hardline Republican, a foreign policy super-hawk and President Donald Trump's pick to replace H.R. McMaster as national security advisor.
Senate confirmation is not required for the White House national security post, and Bolton, a former ambassador to the United Nations, will inherit a staff of several hundred specialists from the Pentagon, State Department and U.S. intelligence agencies.
He will be responsible for advising Trump on a wide spectrum of national security issues, from the U.S.-led coalition against the Islamic State to China's aggressive actions in the South China Sea to North Korea's growing nuclear threat.
Bolton will be the third national security advisor to serve Trump, following the departures of three-star Army generals Michael Flynn and H.R. McMaster.
"It's kind of a head-scratcher, because he seems really out of step with what the president has said and stood for going all the way back to the campaign," retired U.S. Army Lt. Col. Daniel Davis, who served under McMaster during the Persian Gulf War, told CNBC.