Complex sentence: Geoffrey S. F. Ling, M.D., Ph.D., is a medical doctor who retired from the United States Army as a Colonel and currently the Deputy Director for the Defense Advanced Research Projects Agency (DARPA).
Split into simpler sentences: Geoffrey S. F. Ling, M.D., Ph.D., is a medical doctor who retired from the United States Army as a Colonel. He is currently the Deputy Director for the Defense Advanced Research Projects Agency (DARPA).