Sir Steven Charles Cowley Kt FRS FREng FInstP (born 1959) is a British theoretical physicist and international authority on nuclear fusion and astrophysical plasmas. He has served as director of the United States Department of Energy (DOE) Princeton Plasma Physics Laboratory (PPPL) since 1 July 2018. Previously he served as president of Corpus Christi College, Oxford, since October 2016. and head of the EURATOM / CCFE Fusion Association and chief executive officer of the United Kingdom Atomic Energy Authority (UKAEA).