Michael Douglas Griffin is an American physicist and aerospace engineer who served as the Under Secretary of Defense for Research and Engineering from 2018 to 2020. He previously served as Deputy of Technology for the Strategic Defense Initiative, and as Administrator of NASA from April 13, 2005, to January 20, 2009. As NASA Administrator Griffin oversaw such areas as private spaceflight, future human spaceflight to Mars, and the fate of the Hubble telescope.

The Under Secretary of Defense for Research and Engineering, abbreviated USD (R&E), is a senior official of the United States Department of Defense. The USD (R&E) is charged with the development and oversight of technology strategy for the DoD. The post has at various times had the titles Assistant Secretary of Defense for Research and Engineering, or Director of Defense Research and Engineering (DDR&E). The latter title has itself historically varied between the rank of under secretary and that of assistant secretary.