President Trump said Thursday that national security adviser H.R. McMaster, who's resigning, will be replaced by John R. Bolton, a hawkish former United States ambassador to the United Nations.

Quick facts about Bolton:

• Axios' Jonathan Swan reported in early January citing sources saying Bolton is expected to be part "the next phase of Trump's national security team."
• Bolton, a Fox News contributor, will take office on April 9th.
• He served under President George W. Bush as both under secretary of state and ambassador to the UN.
• One area where he and Trump contrast sharply is the Iraq War. Trump has called the war a “huge mistake,” while Bolton insists it was the correct move.
• He and Trump are staunch opponents of the Iran nuclear deal, but Bolton has gone so far as to call for Iran to be bombed. He also wrote a WSJ op-ed last month titled: The Legal Case for Striking North Korea First.
• Bolton served as one of Mitt Romney's foreign policy advisers during his 2012 presidential bid.

Correction: This story has been updated to reflect that Bolton's title was under secretary of state, not assistant secretary of state.