Ridley

Ridley is a dragon-like alien that is one of the main villains in the Metroid series of video games. He is responsible for the murder of Samus Aran's parents. In Super Smash Bros., Ridley can occasionally be seen flying in the background of the Planet Zebes arena.

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 Super Smash Bros. Melee.

Remixes of Ridley's theme music from various Metroid games can be optionally played in the Frigate Orpheon stage in Super Smash Bros. Brawl. He is also a boss fought four times in the Subspace Emissary. The last two times are in The Great Maze.

Role in the Subspace Emissary
In Super Smash Bros. Brawl, Ridley is fought four times in the Subspace Emissary. The first time, he is fought in his normal form by Samus and Pikachu. As the two reach the exit to the facility that contained Samus's Power Suit, 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 well-placed Thunder attack. The battle begins after this. Ridley fights similarly to Master Hand, using many brutal physical attacks. When he is defeated, he falls off the arena.

Later on, Ridley reappears in a cybernetically enhanced form known as Meta Ridley, fighting Samus and Pikachu once again, but now with the additions of Captain Falcon, Captain Olimar, R.O.B., Diddy Kong, and Donkey Kong. This time, he is fought atop Captain Falcon's ship, the Falcon Flyer, as it speeds through a tunnel while trying to escape the floating island before it is engulfed in Subspace. Also, this boss battle features a timer, in which the player must defeat Meta Ridley before it runs out; this is similar to the Meta Ridley battle in Metroid Prime 3: Corruption. This time, Ridley attacks using various fireball-based moves, along with affecting the arena by doing things such as dragging it off-screen.

Soon after Ridley is defeated, the Falcon Flyer escapes, and the floating island is engulfed in Subspace, bringing Ridley with it. In the final level, Ridley and Meta Ridley, along with all the other characters and bosses in the game, must be defeated once more.

Trivia

 * Ridley appeared in Nintendo Monopoly, where he took the place of Tennessee Avenue. He costs $180.
 * Ridley is very similar to King Ghidorah from the Godzilla series. Both are dragons, both are the main villains of their respective series, and both have been reconstructed as a cyborg (Meta Ridley and Mecha-King Ghidorah).