Geoffrey S. F. Ling, M.D., Ph.D., is the CEO of On Demand Pharmaceuticals. He is also a medical doctor who retired from the United States Army as a colonel. He served as the founding director of the Defense Advanced Research Projects Agency (DARPA) Biological Technologies Office from 2014 until 2016. He was considered to be the "US Army's premier subject matter expert on traumatic brain injury (TBI)", and was for years the only neuro-intensive care specialist in the US military.