Guy B. Roberts is an American government official, lawyer, and retired United States Marine Corps colonel who served as the Assistant Secretary of Defense for Nuclear, Chemical, and Biological Defense Programs from 2017 to 2019. He previously was the president of GBR Consulting, a national security consulting firm. Roberts was also a senior associate with the Center for Strategic and International Studies and an adjunct professor teaching courses on homeland security, international terrorism, non-proliferation, and arms control at Mary Washington University and Virginia Commonwealth University. He previously served as the Deputy Assistant Secretary General for Weapons of Mass Destruction Policy and Director of Nuclear Policy for the North Atlantic Treaty Organization. Roberts received the