WASHINGTON — To those who know him, Robert C. O’Brien, the administration’s newest national security adviser, is an ideal choice for the job.

Characterized in national media as an affable, sharp, team player and a tough negotiator, O’Brien is described by those who know him as warm, engaging, receptive, focused and a man of faith.

Raised Catholic and a convert to The Church of Jesus Christ of Latter-day Saints, he will be the highest ranking Latter-day Saint in the U.S. government.

“He is particularly adept at listening to other people, weighing differing opinions and not imposing his own views,” says Sen. Mitt Romney, who has known O’Brien for more than 15 years and sought O’Brien’s insights on military policy during his 2008 and 2012 presidential campaigns.

O’Brien, 53, will be Trump’s fourth national security adviser and was seen as a “safe option.” His management style will be a marked contrast to his predecessor, John Bolton, whom Trump sacked last week after disagreements over the administration’s approach to Iran, Afghanistan and other global challenges. 

At the time of his appointment, O’Brien was the administration’s chief hostage negotiator. He worked closely with the families of American hostages and advised administration officials on hostage issues. He helped secure the release of Andrew Brunson, a pastor held by Turkey for two years and Danny Burch, an oil-company engineer kidnapped in Yemen. He also worked on the case of missing U.S. journalist Austin Tice, who was captured in Syria in 2012. O’Brien has said he is confident Tice is still alive, the Associated Press reported.

Earlier this year, Trump dispatched O’Brien to Sweden to keep tabs on the criminal case there against rapper A$AP Rocky, whom a judge and jury ultimately found guilty of assault in August, several weeks after a street brawl in Stockholm that attracted Trump’s attention.

“He’s worked with me for quite awhile now on hostages and we have a tremendous track record on hostages,” Trump said Wednesday on a tarmac in Los Angeles, hours after revealing the pick on Twitter. “Robert has been fantastic. We know each other well.”

O’Brien, standing alongside Trump, said it was a “privilege” to be picked, the Associated Press reported.

“We’ve got a number of challenges,” he said, adding that the administration’s focus will continue to be on keeping the U.S. safe and rebuilding the military. He said he would advise Trump privately on the situation in Saudi Arabia, where oil facilities were attacked recently by weapons from Iran.

The New York Times reported that O’Brien’s first test as national security adviser may be Iran. Trump has suggested both military action against and negotiations with Iran. On Wednesday, he talked about an economic response.

Romney — who chairs the Foreign Relations Subcommittee on Near East, South Asia, Central Asia and Counterterrorism — called O’Brien “a clear eyed realist. He harbors no prejudice, but he also is very understanding of the maligned intent of nations that are building a military threat.”

Sen. Mike Lee, R-Utah, said he worked with O’Brien when O’Brien was with the State Department.

“He is an incredible champion of religious freedom around the globe and I am confident that he will excel in his role as national security adviser to the president,” Lee said in a statement.

O’Brien has also lent his expertise in international relations to his church, said Matt Ball, public affairs director of the North America West Area of The Church of Jesus Christ of Latter-day Saints.

Ball said he has often relied on O’Brien to help connect the church with foreign diplomats stationed in California to facilitate humanitarian efforts overseas.

“In our experience, he has always been a man who does not tout his contacts or his influence, and yet we never cease to be amazed at the amount of contacts and influencers with whom he has a connection, which is always a wonderful surprise because he’s extremely willing to help,” Ball said.

He recalled a symposium of political pundits during the 2016 election where O’Brien was the only one who predicted Trump would win. Before Trump took office, O’Brien praised him in a column in The National Interest for telling allies to pay their share of the common international defense.

“We may be witnessing the most impressive presidential transition from a national-security standpoint in history,” O’Brien wrote.

He also effusively gave credit to Trump for the hostage releases, which the president cited in calling himself “the greatest hostage negotiator in history.”

But O’Brien has the skills to tell the president what he may not want to hear, said Stephen Larson, who has known O’Brien more than 20 years and co-founded Larson O’Brien LLP, a law firm that focuses on litigation and international arbitration issues, in Los Angeles.

“Good lawyers are very used to telling clients what they need to hear, not what they want to hear, so that’s something that will come natural to Robert,” Lawson said. “By nature, he’s not confrontational, but he never shied away from advising whoever it is on what they need to hear.”

O’Brien has a law degree from the University of California, Berkeley. Before establishing his firm with Lawson in 2016, O’Brien was the California managing partner of the Washington, D.C.-based Arent Fox. 

“He brings with him some unique talents the average person doesn’t have,” said Mike Grow, an attorney with Arent Fox. “He is very focused and has a lot of tenacity and drive to get something done. But he’s very receptive to ideas, not at all dogmatic and has a very practical approach to problems.”

O’Brien’s biography on his firm’s website notes a long resume of public service under the George W. Bush and Barack Obama administrations.

He was the U.S. alternate representative to the United Nations General Assembly from 2005 through 2006, when Bolton was U.S. ambassador to the U.N. In 2008, O’Brien served a three-year term on a government committee that advises on the trafficking of antiquities and other cultural items. He was the founding co-chairman of the Department of State Public-Private Partnership for Justice Reform in Afghanistan from 2007 to 2011 and served under both Condoleezza Rice and Hillary Clinton.

“Earlier in his career, O’Brien was a senior legal officer for the U.N. Security Council commission that decided claims against Iraq that arose from the Gulf War. He was a major in the U.S. Army Reserve,” a State Department biography stated.