Dr. Vergil H. Dykstra
Dr. Vergil Dykstra was the first President of George Mason University who was actually hired for the job. This does not negate the fact that Dr. Thompson was the first President but his appointment mainly came grandfathered in when George Mason College changed to George Mason University. Dr. Dykstra was an outsider from New York. There he was Vice President of the State University of New York's campus. 
This was not the first university that Dr. Dykstra helped transition. Dr. Dykstra took a position with Harpur College for teaching but worked his way up to Vice-President where he then helped Harpur College become Binghamton University. 
While Dr. Thompson did a great job in ushering in the new university there were still some issues such as free speech and academic freedom which some members of George Mason University, students and staff, disagreed with Dr. Thompson's approach, or lack thereof. Dr. Dykstra assured the members of the university that he would tackle these issues head-on. 
 Staff, Mason History Project. "1972-1978: Independence; Changing the Culture at Mason: Dr. Vergil H. Dykstra." A History of Mason. http://ahistoryofmason.gmu.edu/exhibits/show/independence/contents/dykstra.
 Vergil Dykstra Oral History 2009