Complex sentence: Stephen Joel Trachtenberg (born 1937) was the 15th President of George Washington University 1988--2007, and since 1 August 2007 holds the title of President Emeritus and University Professor of Public Service.
Split into simpler sentences: Stephen Joel Trachtenberg (born 1937) was the 15th President of George Washington University, serving from 1988 to 2007. On August 1,2007, he retired from the presidency and became President Emeritus and University Professor of Public Service.