Mark Barr McClellan (born June 26, 1963) is a senior fellow and director of the Health Care Innovation and Value Initiative at the Engelberg Center for Health Care Reform at The Brookings Institution, in Washington, D.C. McClellan served as Commissioner of the United States Food and Drug Administration under President George W. Bush from 2002 through 2004, and subsequently as administrator of the Centers for Medicare and Medicaid Services from 2004 through 2006.