King Dedede

King Dedede (sometimes spelled DeDeDe) is a large penguin-like creature and the self-proclaimed king of Dream Land in the Kirby series, and rival of Kirby. He first appears in Kirby's Dream Land, and has appeared in every game in the series afterward (with the exception of Kirby & The Amazing Mirror). He is somtimes possessed or used as a puppet by other villains in the Kirby series, such as Dark Matter.

Super Smash Bros.
King Dedede makes a minor appearance in Super Smash Bros., as a background element that can be seen flying by on the Dream Land stage.

According to the website, King Dedede was originally planned to be a playable character, but he was cut due to time constraints.

Super Smash Bros. Melee
In Super Smash Bros. Melee, King Dedede makes an appearance as a Trophy. He is also still on the Dream Land stage, which returns from the original Super Smash Bros.

Super Smash Bros. Brawl
King Dedede makes his playable debut in the Super Smash Bros. series in Super Smash Bros. Brawl. In the game, he is voiced by Masahiro Sakurai, his original creator and the director of the Super Smash Bros. series, who also voiced him in Kirby 64: The Crystal Shards. King Dedede is one of the heaviest characters, making him slower, but similar to Kirby, he has multiple mid-air jumps, and has the fastest falling speed of any character. Dedede's hammer gives his moves range and power, but many of his attacks are slow to execute to compensate.

Dedede's neutral special move is Inhale, which works similar to Kirby's move, but Dedede cannot copy opponents, and instead is only able to carry them and spit them back out as a projectile. His side special move is Waddle Dee Toss, in which he throws a Waddle Dee (occasionally a Waddle Doo or rarely a Gordo) at opponents. His up special move is Super Dedede Jump, in which Dedede leaps into the air and slams back toward the ground. His down special move is Jet Hammer, in which Dedede charges a hammer swing powered by a jet engine. Dedede's Final Smash is Waddle Dee Army, which summons Waddle Dees, Waddle Doos and Gordos to attack.

The Subspace Emissary
In the Subspace Emissary, King Dedede finds out about Tabuu's motives, and about his Off Waves, and worries that if all the fighters of this world are all turned into trophies, then there will be no one to change them back. Therefore, he develops special brooches that are set to turn trophies back into fighters after a specific amount of time. It is also revealed through the Smash Bros. DOJO!! that King Dedede engages Meta Knight in combat as the Subspace Army takes his Halberd, though this scene was cut from the final version of Super Smash Bros. Brawl.

He is first seen attacking Luigi with his mallet and turning him into a trophy. However, Wario and his car with the Princess (Princess Peach or Zelda) trophy and Ness trophy come along. King Dedede hides and leaves the Luigi trophy out in the open. Wario takes it, but King Dedede's Waddle Dees come and attack Wario. Wario lets go of the Luigi trophy, which King Dedede takes. After that, he steals Wario's car and drives off with the Princess trophy and Ness trophy. He later attempts to take either the Mario and Pit trophies or the Link and Yoshi trophies, until Kirby shows up, frees them, then all five characters give him a chase. In his castle, he puts a special badge on all the trophies he collected. However, Bowser also starts attacking the others, turning him into a trophy and after some fighting, Bowser escapes with the princess trophy (who dropped the badge King Dedede put on her) and Mario, Link, Pit, Yoshi, and Kirby run away leaving the King Dedede, Luigi, and Ness trophies behind. Later, King Dedede's castle is blown up by the Subspace Bomb. However, the King Dedede, Luigi, and Ness trophies manage to survive. Meanwhile, Kirby finds the other Dedede badge that the princess dropped and swallows it.

The caps actually have the power to turn trophies back to life after some time. After Tabuu turns everyone into trophies, the caps start working and they turn Luigi and Ness back to life, who in turn bring King Dedede back to life as well. King Dedede then decides to help Ness and Luigi save everyone. Meanwhile, Kirby who swallowed the cap is turned back to life. The four go around turning everyone back to life. When King Dedede brings Bowser back to life, Bowser attacks. However King Dedede turns him back into a trophy and then back to life again. Bowser is about to attack again but King Dedede lightly hits him in the nose, then points over toward the staircase to the Great Maze.

Bowser then runs off to attack the Ganondorf trophy because Ganondorf was the one who had turned Bowser into a trophy in the first place. After they are all turned back, everyone, including King Dedede, fights Tabuu. After Tabuu is defeated, the Super Smash Bros. World returns to its normal state and Tabuu disappears.

Super Smash Bros. for Nintendo 3DS / Wii U
King Dedede returns as a playable character in Super Smash Bros. for Nintendo 3DS / Wii U. Several of his moves have been changed from the previous game; most of his aerial attacks are new, his side special has been changed to Gordo Throw, in which Dedede hammers a Gordo to attack opponents, and his Final Smash has been changed to Dedede Burst, which involves Dedede drawing in opponents with his suction breath before hammering them and ending with a bomb exploding on them. While most of his attributes remain relatively unchanged, he no longer has the fastest falling speed.

Dedede also once again appears flying in the background of the Dream Land (64) stage that returns as downloadable content, though he does not appear if he is part of the battle.

Snake's codec

 * Snake: Look at the size of that hammer...
 * Colonel: That's King Dedede you're fighting, Snake.
 * Snake: Dedede? You mean it's not a penguin, Colonel?
 * Colonel: He's the king of Dream Land. Well, so he says, anyway.
 * Snake: Are you sure he's not a penguin?
 * Colonel: One full swing from that hammer can level an entire building. It may look like just a big wooden mallet, but it's actually outfitted with special mechanical systems like turbo jets and precision bearings to boost its effectiveness.
 * Snake: I don't think I could even lift that thing. And he's swinging it around like it was nothing...
 * Colonel: But he also leaves himself wide open. Just make sure you avoid the swing, Snake.

Trophies
Blue indicates exclusive to the Wii U version.

Palutena's Guidance

 * Pit: Who's this, Lady Palutena?
 * Palutena: That's King Dedede.
 * Pit: So what do I need to know about him?
 * Palutena: He's a heavyweight and has the ability to fly. And his hammer attack is no joke. But every fighter has a weakness. For example, when King Dedede throws a spiky Gordo, you can hit it right back at him. If you can eliminate him by reflecting the Gordo, that will count as your KO.
 * Pit: Uh... what's a KO?
 * Palutena: ...Good luck, Pit.

amiibo

 * Every hero needs an arch frenemy, and King Dedede is Kirby’s! He calls himself the King of Dream Land, but he doesn’t have a lot of interest in ruling. His hobbies include eating, stirring up trouble, and yelling orders at his loyal Waddle Dees while bashing things with his huge hammer.