Sometimes you go through life thinking a certain way about a certain person. You think you've got them all figured out, only for them to do something completely unexpected and totally change your mind.
Bad people are sometimes capable of good things and, with the right nurture and care, former delinquents can blossom into law-abiding contributors to society.
Or, sometimes a film studio just runs out of ideas for a sequel and decides to shunt the baddie into the hero role.
That's certainly what happened to these lot. They all started out as the bad guy in one movie, but saw the light in a follow-up.
Now, it's important to stress that "hero" is a very malleable term.
Very few of these monstrous characters completely change their ways and become card-carrying members of the good guy club. It's more complex than that - there is still evil at their core, but they overcome it to do good things and save people instead of tearing them to pieces with a knife.
There is still a bit of that going on, but we're talking about horror movies.
What did you really expect?
9. Jason Voorhees - Freddy Vs. Jason
Rather ironically, considering who's involved, 2003's Freddy vs. Jason was a horror fan's dream come true.
The famous glove-wearing antagonist from the Nightmare on Elm Street series teaming up with Friday the 13th's main villain? This was an absolute fantasy!
It all starts with a dejected Freddy Krueger reviving Jason Voorhees from the dead to assist him in his evil work. Jason soon gets to work slicing and dicing his way through the inhabitants of Springwood, all the while being manipulated by the demon who brought him back to life.
The regular folk in this film orchestrate events leading to Jason and Freddy fighting each other instead, although this doesn't stop them from killing several people in the process. Just as the fight looks to be over and Freddy is about to kill the remaining survivors, Jason emerges from behind him to impale Krueger with his own glove.
Whilst he's not a full blown good guy, Jason is presented as the more sympathetic of the two monsters in this film. He does also make the final save, so we'll give him the benefit of the doubt.