Born in rural Texas, McMillin's natural athleticism shone through early on. He excelled in various sports, but football truly captured his heart. After a standout high school career, he landed at Centre College in Kentucky, becoming a three-time All-American quarterback. McMillin's versatility extended beyond throwing; he was also a formidable safety and kick returner, earning him the nickname "Iron Man" for his all-around talent.

After college, McMillin tasted professional success in the early days of the NFL, playing for teams like the Milwaukee Badgers and Cleveland Indians. However, his coaching career truly cemented his legend. He led various college teams to success, most notably Indiana University, where he won the Big Ten championship in 1945 and was named Coach of the Year.

McMillin's coaching philosophy was ahead of its time. He emphasized offensive innovation, utilizing the forward pass more aggressively than most coaches of his era. He also instilled a strong sense of discipline and teamwork in his players, earning their respect and admiration.

McMillin's legacy extends beyond wins and statistics. He was a pioneer who helped shape the game of football. He was also a respected mentor and motivator, leaving a lasting impact on countless players and coaches.