Ridley, also known by his aliases Geoform 187 and The Cunning God of Death, is a fictional supervillain and one of the main antagonists of the Metroid series. A draconic extraterrestrial hailing from the planet Zebes, he became Samus Aran's archnemesis after murdering the latter's parents as he led a Space Pirate raid on her homeworld. Though having been destroyed numerous times by Samus, he is always resurrected, due in equal part to Space Pirate engineering and his natural regenerative ability, which allows him to swiftly recover from what would otherwise be fatal wounds as long as he is able to consume enough biomatter from his fallen adversaries.

Originally appearing as a subordinate of Mother Brain (another primary antagonist), he returns in Metroid Prime and Metroid Prime 3: Corruption in his cybernetic Meta Ridley form, commanding the Space Pirates himself. He is fully sentient and he can also speak in the Metroid e-manga.

He is named after Ridley Scott, director of the 1979 film Alien, which has been described by character designer Yoshio Sakamoto as a "huge influence" on the world of the Metroid series.