WASHINGTON (AP) — 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. O’Brien, who made headlines in July when he was dispatched to Sweden to monitor the assault trial of American rapper A$AP Rocky, was among five candidates Trump said Tuesday were under consideration.

“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.

“We’ve had tremendous foreign policy successes under President Trump’s leadership. I expect those to continue. We’ve got a number of challenges,” he added. O’Brien said 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.