This one could've been subtitled, "when appearances aren't deceiving".
Wrestling is full of frightening characters, but most of them are fictional. For example, by all accounts, Glenn Jacobs is a lovely chap who is nowhere near as scary as his Kane character has been for decades on screen. Away from the ring, he's a true gent, and he's one of many false brutes able to separate ring from reality.
This list isn't preoccupied with those who perhaps raise hairs on the back of fan necks though. It's more about those workers who terrified the living crap out of others they shared locker rooms with. There are some seriously chilling souls here, ones who either loved playing up to reputations or were legitimate bad asses who would rather rip someone's face off than talk it out if things got heated.
They all share one thing in common. Every single one had several peers running for the hills or staying up the night before matches with acid reflux at the thought of stepping inside the ring with them. Welcome to pro wrestling's own personal (shoot) 'Hall Of Horrors'...