President Donald Trump announced on Twitter Wednesday Robert C. O’Brien will be his new National Security Advisor. He is the fourth National Security Advisor since Trump took office and is replacing John Bolton, who was fired from his position this month. The position does not require confirmation by Congress.

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. I have worked long & hard with Robert. He will do a great job! — Donald J. Trump (@realDonaldTrump) September 18, 2019

Bolton and Trump were at major impasses on issues such as Venezuela, Iran and North Korea. Bolton noted in a Tweet this month that he offered to resign before Trump fired him. It will be interesting to see how O’Brien works under Trump. He is not as well known as the previous national security advisors but has a stellar history with the State Department and a long list of qualifications.

Five Quick Facts You Need To Know About Robert O’Brien.