Kevin Plank founded the performance sports apparel company, Under Armour (NYSE: UA) (NYSE: UAA), on an idea that he had as a walk-on football player at the University of Maryland. The story goes that the cotton T-shirt Plank wore under his uniform would hold so much sweat, he felt it slowed him down. He was determined there had to be a better way. Over twenty years later, that idea has grown into a $5 billion global business that competes against industry giants Nike and Adidas.