Donald Trump has named Robert C. O'Brien, the State Department's top hostage negotiator, as his new national security adviser.
O'Brien will replace John Bolton, who was ousted last week amid a difference of opinion with the US president.
Bolton was often described as a "hawk" and known for his tough stance on Iran. He was also an arms control adviser in the Bush administration and advocate for the Iraq war.
O'Brien will be Trump's fourth national security adviser in his less than three years as president.
Who is Robert C. O'Brien?
O'Brien is currently the US special presidential envoy for hostage affairs in the State Department.
He recently appeared in a Stockholm court on behalf of A$AP Rocky after the rapper was detained in Sweden.
After Danny Burch, a US hostage held captive in Yemen for 18 months was released, Trump celebrated in the Oval Office, where O'Brien praised the US president.
"The president has had unparalleled success in bringing Americans home without paying concessions, without prisoner exchanges, but through force of will and the goodwill that he’s generated around the world," he said.
O'Brien has advised several well-known Republicans in foreign policy including former Wisconsin Governor Scott Walker during his 2016 campaign, former Republican presidential candidate Mitt Romney and Texas Senator Ted Cruz.
He's a trial lawyer from California who worked in both the Bush administration and Obama administration.
He served as the US alternate representative to the UN General Assembly while Bolton served as US ambassador from 2005 to 2006.
At the US State Department, he co-founded a justice reform partnership for Afghanistan which he worked on from 2007 to 2011 under both Secretaries Condoleezza Rice and Hillary Clinton, according to a biography posted by his LA-based law firm, Larson O'Brien.
The law firm also states that O'Brien has worked on several high profile entertainment cases and represented A-list celebrities in intellectual property rights cases.
Views on foreign policy
In a 2016 book on the United States' role in the world entitled While America Slept, O'Brien is very critical of former US President Barack Obama's foreign policy. The book examines what he calls an America "in retreat" and argues for a "more involved" American role in foreign affairs.
O'Brien, like US President Donald Trump, is extremely critical of the 2015 Iran Nuclear Deal — that placed limits on Iran's nuclear programme in exchange for a lifting of sanctions.
O'Brien called the Iran Deal "Obama's folly" and a disaster, comparing it to UK Prime Minister Neville Chamberlain's 1938 Munich Agreement which is seen as having appeased and emboldened Adolf Hitler by allowing him to annex a part of Czechoslovakia.
O'Brien wrote in his 2016 book: "there is simply no evidence to support the idea that we can trust revolutionary Iran to give up its long-term goal of developing a nuclear weapon and delivery systems."
In terms of his hostage work for the State Department, O'Brien wrote in an article in late 2018 that Iran is the "worst kidnapper of Americans".
"Iran, either directly or through Hezbollah or its other proxies, has kidnapped American diplomats, hikers, students, tourists, naturalized United States citizens visiting their families in Iran, businessmen, and sailors. Iran sadly continues this uncivilized and unethical conduct even today," O'Brien wrote in an editorial published by the Los Angeles-based foreign policy organisation Pacific Council on International Policy where O'Brien is a member.
In O'Brien's 2016 book, he is also highly critical of Western countries' response to actions by Russia and China, stating that they've appeased them:
"The authoritarian powers, Russia and China, have the initiative and are on the move. They are, in turn, watched by a regional provocateur, Iran, which has its own visions of Middle Eastern hegemony," O'Brien writes in a book chapter that was originally published in 2014.