Mollenkopf was a successful football coach competing at high school and college levels and is widely acknowledged as the greatest football coach in Purdue's history. While coaching high school, he led Toledo Waite to three national championships. Mollenkopf is Purdue's all-time leader in Big Ten Conference wins (58) and conference winning percentage (.637). His 84 wins at Purdue placed him first on the school's all-time wins list until Joe Tiller passed him in 2008, and he ranks fourth in overall winning percentage (.670). Mollenkopf's Boilermakers were nationally ranked for 80 weeks, the most under any Purdue head coach, and captured the #1 spot the first five weeks of the 1968 season.