Washington, September 18 (RHC)-- U.S. President Donald Trump has named Robert O'Brien as his national security advisor, eight days after the abrupt departure of John Bolton.  O'Brien, the State Department's top hostage affairs official, will become Trump's fourth national security advisor, following the departures of Bolton and retired Army Gens. Michael Flynn and H.R. McMaster.

While O'Brien's recent work primarily dealt with matters involving U.S. hostages, he was assigned by Trump to help free rapper A$AP Rocky, who was detained in Sweden on assault charges over the summer.  The rapper was found guilty, but was spared from jail time.

O'Brien was also a partner in a boutique law firm focusing on high-stakes trials and appeals, and was a foreign policy advisor to Mitt Romney during the Utah senator's presidential run against then-President Barack Obama in 2012.  O'Brien attended an Oval Office event in March, where Trump greeted a freed U.S. citizen who had been held in Yemen.  The president called O'Brien "the greatest hostage negotiator in our history" at that event.

Trump on Tuesday had named O'brien and four other finalists for the role, including Vice President Mike Pence's national security advisor Keith Kellogg and Bolton's former chief of staff, Fred Fleitz.  In selecting O'Brien, Trump said: "I have worked long & hard with Robert. He will do a great job!"

The national security advisor does not require Senate confirmation.  The position comes with a staff of hundreds of specialists from the Pentagon, State Department and U.S. intelligence agencies.

Robert O'Brien's ascension comes as the Trump administration has pulled the United States back from global commitments and pushed forward on ambitious projects like the denuclearization of North Korea, a growing military footprint on the southwest border with Mexico, rising tensions with Iran, a bitter trade war with China and a recently aborted effort to negotiate the end of the U.S. war in Afghanistan.