The original prototype for Super Smash Bros. was a four-player fighting game designed by Masahiro Sakurai and programmed by Satoru Iwata tentatively called "Dragon King: The Fighting Game". The game was designed specifically for the Nintendo 64's joystick to see how it could be used in a multiplayer environment. The signature concept of Nintendo characters fighting each other was not initially present, but would soon be implemented as the first idea Sakurai thought of to make his game stand out, as fighting games did not sell well and most of his original concepts felt better suited for arcade fighting games rather than home-console fighting games. A subsequent prototype featuring Mario, Donkey Kong, Samus, and Fox as playable characters was then made without sanction from Nintendo's higher-ups and they were not informed of its existence until Sakurai was sure the game was well-balanced. When Iwata initially presented the idea of the game to Shigeru Miyamoto to gain approval for the use of Nintendo characters, he turned it down. However, Iwata did not tell Sakurai this and convinced him to pitch the prototype to Miyamoto anyway, which later got his approval.

Little is known about Dragon King's gameplay or design, and all information known about the game comes from interviews and a handful of images shown when the game was in an alpha stage. No gameplay footage has been demonstrated, and a working prototype has not been made publicly available. Images of the game, however, show that much of the core gameplay was similar to Super Smash Bros., featuring damage percents, arenas with platforms, and combatants that do not strictly have to face one another. The tall, thin build of the unnamed fighters and their kicking and punching techniques also appear to be relatively similar to that of Captain Falcon. The most widely-known stage background featured in the screenshots is a photo taken by Sakurai of a Ryūō-chō neighborhood in Yamanashi, Japan, which is where HAL Laboratory's headquarters are based, where the game was being developed, and what the prototype was named after. The "Ryūō" in Ryūō-chō means "Dragon King".