character everyone fears will destroy the world actually does

There are a lot of plots in which everyone is afraid of a character who is supposed to be very dangerous and/or destroy the world, but that character never actually is as bad as everyone expects (usually because they don't want to do those things). The closest I've seen a character actually do what everyone feared was the FL in Love and Redemption.

So, I'm curious, are there any movies or dramas in which the character is as bad as/does exactly what everyone fears?

 Lou:

Attack on Titan lol 

LMAO

Thank you!