Back in 2001, as part of an initiative to revitalize Madison Square Park, Danny Meyer set up a simple hot dog cart. At that time, he had been a leader in New York City's fine dining scene for years, and the hot dog cart was just a side project, something fun to do for the summer. But that one temporary hot dog cart led to Shake Shack, a fast casual restaurant chain known for its burgers, its namesake milkshakes, and its lines out the door. Today, Shake Shack is a publicly traded company with over 250 locations in 15 countries.