The game features eight of the most famous and successful heavyweight boxers in history: Muhammad Ali, Jack Dempsey, Joe Frazier, Larry Holmes, Evander Holyfield, Joe Louis, Rocky Marciano, and Floyd Patterson. There are also a total of thirty other imaginary fighters present in the game. The cartridge supports the 6 button control pad (an improvement over the controller options of its predecessor). Source: Wikipedia, "Greatest Heavyweights of the Ring", available under the CC-BY-SA License.