Ridley is a recurring dragon-like antagonist in the Metroid series, appearing in some form in all but three Metroid games (Metroid II: Return of Samus, Metroid Prime Hunters, and Metroid Prime 2: Echoes). He is the leader of the Space Pirates' military.
Throughout the series, Ridley has appeared in various incarnations, including a cybernetically enhanced version and a Phazon-mutated form, as well as mechanical and bio-engineered clones. Though he has never had any dialogue in-game, in the official Metroid manga, Ridley is capable of speech.
Ridley's most recent appearance was Metroid: Other M. Aside from main-series Metroid games, Ridley has also appeared in every Super Smash Bros. game (though two are cameos) and the Metroid manga.