Heavystep

He's an immortal man who has been teaching his apprentice, Dawnpaw, how to be immortal. He failed, and StarClan made a prophecy about him.

"Someone who is immortally heavy shall fail when trying to add on to the immortal society."

Turns out, Crookedstar was smoking something he shouldn't have and also lost a bet on Twitter, and he was forced to make this prophecy. It was fake, and Heavystep was able to teach Mistystar and Purdy how to be immortal. He then became king of ImmortalClan because he is awesome.