Ridley

Ridley is a high-ranking member of the Space Pirates, and one of the main villains in the Metroid franchise. He is directly responsible for the murder of Samus Aran's mother and partially responsible for the death of her father. In several instances, Ridley appears as an upgraded cybernetic version of himself called Meta Ridley.

Super Smash Bros.
In Super Smash Bros., Ridley can occasionally be seen flying in the background of the Planet Zebes arena.

Super Smash Bros. Melee
Ridley also makes a brief appearance in the opening cinematic of Super Smash Bros. Melee, where he can be seen battling his archenemy, Samus Aran. A Trophy of Ridley can also be obtained in this game.

Super Smash Bros. Brawl
In Super Smash Bros. Brawl, Ridley is fought twice in The Subspace Emissary.

The first time he is encountered, he is fought by Samus and Pikachu. As the two reach the exit to The Research Facility, where her Power Suit had been held, Ridley appears without warning and snatches up Samus. Roaring, he slams her into a wall and drags her along it. Pikachu comes to Samus's rescue, hitting the space dragon with a Thunder attack, after which the battle begins. Ridley fights similarly to Master Hand, using many brutal physical attacks. When he is defeated, he falls off the arena.

He later reappears as Meta Ridley, attacking a group including Captain Falcon, Captain Olimar, R.O.B., Samus Aran, Pikachu, Diddy Kong, and Donkey Kong as they try to escape the Isle of Ancients before it is engulfed in subspace.

As this battle is fought while trying to escape an island, there is a set time limit of two minutes that the player has to defeat Meta Ridley, who is more difficult to beat than Ridley was. Additionally, there is the added difficulty of the battle taking place on top of Captain Falcon's ship, the Falcon Flyer, so it is possible for the player to fall off the edge and lose.

Meta Ridley uses some of the same attacks as Ridley did, such as scraping his tail across the top of the Flyer and firing fireballs, but also shows additional ones that involve grabbing the Falcon Flyer and lowering it down with his weight, sometimes even lowering it off of the screen. Fortunately, most of Meta Ridley's attacks can be avoided by jumping off the Falcon Flyer at the right time. Meta Ridley's fireballs can also be reflected right back at him.

If the player manages to defeat Meta Ridley, a cutscene is shown, and the Falcon Flyer escapes while the island is engulfed into subspace.

Both fights are reprised in The Great Maze with any characters that have been rescued throughout the Subspace Emissary. He is also fought in the Boss Battles game mode. There is no time limit when fighting Meta Ridley in either The Great Maze or in Boss Battles mode.

Super Smash Bros. for Wii U
In Super Smash Bros. for Wii U, Ridley is a stage hazard boss on the Pyrosphere stage. His physical appearance, like Samus's, is based on his appearance from Metroid: Other M. Once attacked enough by a player, Ridley allies with that player, and attacks the other players. He can also transform into Meta Ridley by absorbing enough energy. He can be defeated, and, as if he was a character, defeating him rewards the player with a K.O. point; he can be defeated by his own ally as well.

There is a trophy of Ridley that can be unlocked if the player's fighter deals the finishing hit to a boss in Smash Tour.

Super Smash Bros. Ultimate
In Super Smash Bros. Ultimate, Ridley is a playable character for the first time, announced during the E3 2018 Nintendo Direct alongside fellow newcomers Inkling and Daisy. His appearance in this game seems to primarily be based on that in Super Metroid, while he has a similar size to his appearance in the original Metroid. His Final Smash involves him slamming an opponent or opponents against Samus's Gunship and shooting plasma at the ship; the falling gunship can be seen in the background after the attack. Two of his alternate costumes swap him out for Meta Ridley (although he is still referred to in-game as simply "Ridley").

Ridley does not share a victory theme with Samus, instead using an intense and sinister variation of the Metroid victory theme; the flourish itself is shared with Dark Samus, and this trait is shared with fellow newcomers Chrom, King K. Rool, and Piranha Plant, as well as several veterans, namely Meta Knight, Bowser, Bowser Jr. (and the Koopalings), Rosalina & Luma, Dark Pit, Robin, Lucina, and Corrin.

In Ridley's reveal trailer, A Piercing Screech, Mario, Mega Man, and Samus Aran are traversing through a mechanical room on a walkway. Ridley stealthily takes Mega Man and Mario out by impaling the former with his tail and crushing the latter's head. Samus eventually senses something amiss and points her arm cannon behind her, only to find Mario's discarded hat. Suddenly, the walkway quakes with Ridley bursting out from underneath and knocking a shocked Samus off her feet. Ridley then proceeds to roar before giving an inhuman smirk as he twirls Mario's hat around his finger. In the ending of the trailer, Ridley, after presumably causing a blaze to kill Samus, is flapping his wings only to glare in slight irritation when Zero Suit Samus uses her Jet Boots to leap from the blaze and descend down to attack him.

Ridley is a heavy fighter, being heavier than Snake, R.O.B., and Banjo & Kazooie but lighter than Samus, Bowser Jr. (and the Koopalings), Dark Samus, and Terry, while having the same weight as Wario, Ike, Simon, and Richter.

Palutena's Guidance

 * Pit: RIDLEY CONFIRMED!
 * Palutena: Uh, yes. That's Ridley. Samus's archnemesis.
 * Pit: I never thought I'd have to fight an alien space dragon in Smash...
 * Viridi: Kirby's a space alien too, ya know! Jury's still out on him being a dragon, though.
 * Palutena: Ridley may look like a mindless killing machine, but he's exceedingly intelligent. He's also the leader of the ruthless Space Pirates.
 * Pit: So what's the story behind him and Samus?
 * Palutena: Ridley killed Samus's parents when she was young.
 * Pit: That's messed up!
 * Palutena: Samus and Ridley first fought in the depths of Norfair on Planet Zebes. They crossed paths again when Ridley stole the Baby Metroid. Meta Ridley was made through genetic engineering and cybernetic enchancements. Omega Ridley is the one infused with Phazon... Neo-Ridley was born when an X parasite absorbed Ridley's genes. And yet another Ridley was created by cloning cells found on Samus's suit!
 * Pit: You sure know a lot about Ridley. And none of it is about how to fight him!
 * Viridi: There's also a robot version of Ridley. He built it himself, which officially makes him a narcissist.
 * Pit: Is that canon?
 * Palutena: Canon or not, all of these Ridleys shared the same fate-they were all defeated by Samus.
 * Pit: Not surprising. Samus is a beast!
 * Palutena: So is Ridley. Mind the sharp barb on his tail.

amiibo

 * Ridley is the leader of the Space Pirates in the Metroid™ series and Samus’s long-standing rival in battle. He looks like a pterosaur but has high intelligence and a brutal nature. Ridley utilizes wings for a full range of flight and attacks with fireballs from his mouth and whips of his tail.

Super Smash Blog bio

 * Joining the battle from the storied Metroid series, Ridley's long tail and sharp claws let him unleash a torrent of devastating attacks. His Final Smash is a powerful stream of plasma breath intense enough to bring down Samus's starship.

Trivia

 * Ridley's trophies in Super Smash Bros. Melee and Super Smash Bros. Brawl both state that he is the head of the Space Pirates on Zebes. This is false since the real head is Mother Brain and the Space Pirate Command.
 * Ridley's stock icon for Super Smash Bros. for Wii U uses his appearance from Super Smash Bros. Brawl instead of his Metroid: Other M appearance.
 * Ridley's stock artwork in Super Smash Bros. Ultimate resembles from Super Smash Bros. for Nintendo 3DS / Wii U.
 * Ridley's splash screen introduction in his Super Smash Bros. Ultimate reveal trailer; "Ridley Hits the Big Time!", may be a reference to "Ridley is Too Big", an Internet meme originating from arguments against Ridley being a playable character in the Super Smash Bros. series.
 * Many people believed Ridley would be a playable fighter in Super Smash Bros. Brawl, but in an interview with Nintendo Power, Masahiro Sakurai stated that he never considered him a playable character at all when designing the game.
 * His appearance in Super Smash Bros. Ultimate is the first game to directly showcase his more intelligent and cunning personality traits, as while various sources in both prior Super Smash Bros. games and his home franchise (most directly in the Metroid manga) strongly implied that he possessed these traits, they were not immediately apparent in his characterization in the games, where he is generally portrayed as simply a monster.