President Trump last week named Ambassador Robert C. O’Brien, a Pasadena resident, as his fourth National Security Advisor. Trump made the announcement on Twitter while visiting Los Angeles.

“I am pleased to announce that I will name Robert C. O’Brien, currently serving as the very successful Special Presidential Envoy for Hostage Affairs at the State Department, as our new National Security Advisor,” Trump tweeted. “I have worked long & hard with Robert. He will do a great job!”

O’Brien enters an administration mired in chaos as House Speaker Nancy Pelosi announced the launch of a formal impeachment inquiry against the president on Sept. 24. In August, a whistleblower in the intelligence community filed a complaint against the president for allegedly pressuring incoming Ukrainian President Volodymyr Zelenskiy to investigate Trump’s potential political rival in the 2020 election, former Vice President Joe Biden and his son Hunter, and allegedly threatening to withhold hundreds of millions of dollars in military aid to Ukraine if they didn’t comply with Trump’s request.

The move to hire O’Brien came shortly after the departure of Trump’s previous National Security Advisor, Ambassador John Bolton. Trump said he fired Bolton, while Bolton insisted that he offered to resign first. The two disagreed about a number of foreign policy issues, including Afghanistan, Iran and North Korea. O’Brien has similar ideological views as Bolton, though he is much less confrontational and is well-liked by those who know him.

As Trump’s hostage negotiator, O’Brien led the US government’s diplomatic efforts to secure the release of Americans held hostage worldwide while liaising with their families in the United States. A conservative Republican, he has served in both Democratic and Republican administrations in State Department positions and as a representative to the UN General Assembly under Bolton. He was also a major in the US Army Reserve.

O’Brien is the co-founding partner of Larson O’Brien LLP in Los Angeles, a litigation firm that focuses on international arbitration. Before moving to Pasadena, O’Brien lived for many years in La Cañada Flintridge. He had two sons, one of whom tragically drowned in 2015. O’Brien converted from Catholicism to Mormonism in his 20s, and is the author of the 2016 book, “While America Slept: Restoring American Leadership to a World in Crisis.” He has long argued for expanding the U.S. military, particularly the Navy.

In 2016, O’Brien laid out what he thought the incoming 45th president’s foreign policy priorities and national security agenda should be in an article for the Pacific Council on International Policy, an independent, nonprofit and nonpartisan organization in Los Angeles dedicated to foreign affairs. He argued that the new president “must commit to a national security policy of ‘peace through strength,’ reassert American leadership, and rebuild our alliances.” He has been a member of the Pacific Council since 2007.

While he was not a “Never Trump” Republican, O’Brien also wasn’t a full-fledged Trump supporter from the beginning. During the 2016 Republican primary season, O’Brien served as foreign policy adviser to the failed presidential bids of Wisconsin Gov. Scott Walker and then Texas Sen. Ted Cruz. O’Brien also served as a senior adviser to then-Massachusetts Gov. Mitt Romney’s presidential campaigns in 2008 and 2012, and considers himself a traditional Reagan Republican who warns against isolationism.

“Ambassador Robert O’Brien has been a valued member of the Pacific Council for over a decade,” said Dr. Jerrold Green, president and CEO of the Pacific Council. “His long career of public service, as well as recent successes as Special Presidential Envoy for Hostage Affairs at the US Department of State, have been characterized by great integrity, commitment, effectiveness and success and the country is lucky to have Robert as its new National Security Advisor.”