Ridley

Ridley is possibly the most well-known villain from the Metroid Series.

Background Information
Ridley is the most recurring character in the Metroid Saga, as he has appeared in nearly every Metroid game to date (He was left out of only Metroid Prime 2: [Dark] Echoes, and Super Metroid). His common appearance has led to the idea that there are multiple Ridleys, each being cloned off of the first. This is a possibility, as is the idea of there only ever being one Ridley.