In October 1973, twelve of the top drivers in the world were invited to compete in IROC, the International Race of Champions, an event penned by the legendary Roger Penske. The drivers were selected from the four major racing series at the time, Formula One, NASCAR, SCCA, and USAC, and included names such as Mark Donohue, George Follmer, A.J. Foyt, Richard Petty, and Bobby Unser. All were to drive the same car, as the goal of the event was to reduce variables such as the vehicle and its modifications and to put emphasis on the skill and race strategies for the drivers. Penske’s vehicle of choice was the Porsche 911 RSR.