Ridley is Samus Aran's favorite buddy to shoot apparently. This bad dragon is known to practically everyone who played the series.
He's evolved a bit over the years. At first they were going to make him look like this.
But he ended up like this on Metroid for NES.
He truly became awesome in Super Metroid. He gave me one of the best boss fights that I can remember.
Ridley would stay in a slumber since Metroid missed the N64. He first real appearance since Super Metroid was a cameo in Super Smash Bros. Melee.
He later returned even better in Metroid Prime.
And he's stayed in practically every Metroid related thing ever since. Including more cameos.