President Donald Trump on Wednesday named Robert O'Brien, his chief hostage negotiator and an established figure in Republican policy circles, as his new national security adviser.
O'Brien, the fourth person in two years to hold the job, becomes the administration's point person on national security amid rising tensions with Iran following the weekend attack on Saudi oil installations and fresh uncertainty in Afghanistan after the halt in peace talks with the Taliban.
The announcement of O'Brien's selection comes a week after Trump ousted John Bolton from the post, citing policy disagreements.
"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!"
Trump abruptly forced out Bolton on September 10, after he and his hawkish national security adviser found themselves in strong disagreement over the administration's approach to Iran, Afghanistan and a host of other global challenges.
O'Brien comes into the new job with backing from Secretary of State Mike Pompeo and senior Republicans in Congress.
As the special presidential envoy for hostage affairs at the State Department, O'Brien worked closely with the families of American hostages and advised administration officials on hostage issues. He helped secure the release in February of American citizen Danny Burch, who was freed after 18 months in captivity.
He has also worked on the case of missing US journalist Austin Tice, who was captured in Syria in 2012. O'Brien has said he is confident Tice is still alive though it's unclear who is holding him.
The White House sent O'Brien to Sweden to monitor the case of A$AP Rocky, who was charged with assault. The rapper, whose real name is Rakim Mayers, was permitted to return to Los Angeles to await the verdict of a Swedish court that found him guilty in a street brawl.
Last month, the wife of a Princeton University graduate student detained in Iran told reporters that she would like to see the same level of personal attention from the government as A$AP Rocky received.
O'Brien previously helped lead the department's public-private partnership for justice reform in Afghanistan during the Bush and Obama administrations.
From 2008 through 2011, O'Brien was a presidentially appointed member of a government committee that advises on issues related to the trafficking of antiquities and other cultural items. In 2005, President George W. Bush nominated O'Brien to be US Representative to the UN General Assembly, where he worked with Bolton. O'Brien was confirmed by the Senate.
He also was an adviser on the Republican presidential campaigns of former Gov. Scott Walker of Wisconsin, former Gov. Mitt Romney of Massachusetts and Sen. Ted Cruz of Texas.
Earlier in his career, O'Brien was a senior legal officer for the UN Security Council commission that decided claims against Iraq that arose from the Gulf War. He was a major in the US Army Reserve.
O'Brien has a law degree from the University of California, Berkeley, and co-founded a law firm in Los Angeles focused on litigation and international arbitration issues.
In his 2016 book "While America Slept," O'Brien criticized what he called then outgoing president Barack Obama's attempt to present a more collaborative, dovish United States.
This meant "autocrats, tyrants, and terrorists were emboldened," he argued.
"In the face of rising challenges around the world, it is time to return to a national security policy based on 'peace through strength,'" he wrote.
"A strong America will be a nation that our allies will trust and our adversaries will not dare test."