King Bowser Koopa, known in Japan as Great Demon King Koopa (大魔王クッパ, Daimaō Kuppa), sometimes known as King Koopa, is a large character and usually the main antagonist of the Mario series. Bowser makes an appearance in the Flash-cartoon series, A Super Mario World taking his usual role as one of the primary antagonists. He is also one of the many playable characters in Super Smash Flash 2, and has been classified as one of the heaviest characters in the game.
In Super Mario Bros., his first appearance, Bowser appears at the end of each of the eight worlds (Level X-4). These areas are "dungeon stages" and are characterized by white brick platforms, ample lava and spinning sticks of fire that can burn Mario/Luigi. Bowser waits at the end, on a bridge over a pool of lava. By grabbing the axe at the right end of the bridge, Mario/Luigi can cut the rope at the end, making the bridge collapse and sending Bowser into the pit of lava below. Alternatively, Bowser can also be defeated by repeatedly shooting him with Fire Breath. Due to graphic limitations, the in-game Bowser does not seem to have hair, although the official artwork for the game, as well as the remake in Super Mario All-Stars, depicted him with hair. Bowser throws hammers in Super Mario Bros., similar to the Hammer Bro., but this ability has largely been dropped; exceptions being throwing hammers with magic in Princess Peach, and he also threw hammers at the beginning of Super Mario RPG: Legend of the Seven Stars, and uses them as his primary attack in Mario & Luigi: Superstar Saga when he is teaming up with Popple, while Dry Bowser in New Super Mario Bros. and New Super Mario Bros. Wii throws bones in a similar manner.
Though Bowser appears in the sequel to Super Mario Bros. (a title known outside Japan as Super Mario Bros.: The Lost Levels), he appears and behaves identically to his original incarnation. Only in Super Mario Bros. 3 did Bowser return with a new plot and a new look. For the first time in the games, players saw Bowser with a mane of red hair, a look that has remained with Bowser ever since. This time, Bowser only appears at the end of the final level: his castle at the end of World 8, where Mario and Luigi have to trick him into crashing through his floor in order to defeat him (although he could also be defeated with several fireballs or hammers.) This game also introduces Bowser's first seven children, the Koopalings. Despite the presence of offspring, no mate of Bowser has appeared in any story, and his only known relationship is his marriage to a reluctant Princess Peach in Super Paper Mario.
In A Super Mario World
Bowser is seemingly the main antagonist in McLeodGaming's Flash animated short series, A Super Mario World. He only appears during the second episode of the series, but he is first mentioned during the events of the first episode, where it is revealed he has kidnapped Princess Zelda in order to lure Link and Mario into a trap. He has also allied with Sega fellow characters Sonic the Hedgehog, Knuckles the Echidna and Doctor Eggman, the first two acting as his personal guards with the latter helping him to improved his castle into a flying mechanical unit called the "Bowser-Eggman Cruiser". After Mario and Link defeat Knuckles and Sonic (who had previously transformed into Super Sonic) with the help of Cloud Strife, they chase after Bowser on the roof of his castle, where everything is revealed. Bowser informs the heroes he is not the mastermind behind Zelda's kidnapping but that everything was a trap set by Riku in order to kill the three heroes. Bowser proceeds to free Zelda as she in no longer useful to him, this act infuriates Link, who quickly decapitates Bowser with his sword.
Bowser is a playable character in the SSF's reboot, Super Smash Flash 2. While being "confirmed" for the initial roster many years back, he was shelved by the developers following a change in the game roster. After that, Bowser could be numerously spotted on a few pages on the Smash Flash DOJO!!!, prompting many fans to believe he would be in the game after all, however, developers stood once again claiming that was not the case and that Bowser still was not confirmed for the game despite the images, which were utterly removed when the DOJO!!! got revamped. Bowser was ultimately confirmed to be playable in the second McLeodGaming Direct. Throughout his development history, Bowser has carried different sprite designs, the first ones were taken from his appearance in Mario & Luigi: Partners in Time, the second sets were taken from Super Princess Peach, but his third and final designs — the ones he uses in-game — are completely custom made. Bowser's attributes, and overall sprites' appearance mixes elements from Super Smash Bros. Brawl and Super Smash Bros. for Nintendo 3DS and Wii U.