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.

In Super Smash Bros. Brawl, Ridley is a boss fought a total of two times in the subspace emissary; once on the floating Isle of the Ancients, by Samus and Pikachu, and once again in The Great Maze; by any characters that have been rescued.

Remixes of Ridley's theme music from various Metroid games can be optionally played in the Frigate Orpheon stage in Super Smash Bros. Brawl.

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.

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).