The Greatest Rivalry in sports.
It all goes back to Woody Hayes and Bo Schembechler.
Bo was Woody's assistant and Woody promised he would retire soon, every year just to keep Bo around. Finally, he left for the head coach of the arch-rival and they entered the 10-Year War between them.
Actually they were dear friends, but truly despised each other on the other side of the field. When Woody died of cancer, Bo was at his side in the room until the end.
Woody made the phrase "that State up North" popular because he would never even dignify it by stating the name "Michigan."