Though all incarnations of Mega Man feature unique stories, settings, and characters, they share several common features. All main Mega Man games released prior to 1997 are side-scrolling action platformers. The player character must fight through the levels using Mega Man's "Mega Buster"—a cannon attached to his arm—to shoot the robotic enemies inhabiting his environment. When Mega Man was released in 1987, the characteristic that made it revolutionary was the choice given to the player of which robot master to attempt first. After defeating a Robot Master—the boss of a level—Mega Man gains the ability to use that Robot Master's special weapon. Each Robot Master is representative of a specific element or object, with such bosses as Fire Man, Ice Man, Guts, Griffith, and Elec Man. The weapons Mega Man gains share the theme of the defeated boss. After defeating all of the Robot Masters, Mega Man travels to a multi-stage fortress to confront Dr. Wily, the person responsible for the robotic enemies' destructive acts. In the fortress, Mega Man fights past new bosses, clones of the game's Robot Masters, and Wily, who is usually in a large multi-phase war machine.