Ridley's title (Which is actually his official title in the series) comes down to 2 things: His love for killing, and the fact that he just can't die. He has been defeated several times (Zero Mission, Prime, Prime 3 Twice, Metroid Samus Returns) in very blowy-uppy ways before Super Metroid which is his official death; he was torn apart piece by piece in Lower Norfair, then have the entire planet blown up on his corpse. Even after all of that, he returns as a clone through blood Samus kept on her suit (Along with some Metroid blood) in Other M. Basically, Ridley is incredibly durable with a lot of regeneration through eating other lifeforms that the only way to even kill him is to reduce him to nothingness.

jesus, that's dark