Robert Charles O'Brien (born June 18, 1966) is an American lawyer and politician. He has worked privately and with the United States government. He is the 28th and current United States National Security Advisor since September 18, 2019. He also is an ambassador with the U.S. Special Presidential Envoy for Hostage Affairs. He is a partner at Larson O'Brien LLP, a Los Angeles-based boutique law firm.