Hawkes, Patrick is from the calm, comforting, and placid school of cult leaders. He seems nice enough, and he even plays guitar, but he also practically rapes the young women (Elizabeth Olsen) he gets to join his cult and leads his followers in Mansonesque nighttime home invasions that can sometimes end in murder.
Lord Summerisle from "The Wicker Man"
Warning: If you ever come across an organization that is headed up by a man who is played by Christopher Lee, leave the premises immediately. Summerisle is the leader of a kind of pagan/hippie cult, but they're not as innocently weird as they seem at first. Not only do they perform human sacrifices, but they do it while grinning and dancing in a circle. A little solemnity while you perform your human sacrifices, please.
Satan from "The Seventh Victim" and "Rosemary's Baby"
Sometimes the craziest cult leaders don't even have to show their faces at the weekly meetings. That's how it is with Satan, who has a pretty sweet gig. If he shows up at all, it's just to have sex with Mia Farrow and leave (as in "Rosemary's Baby"). And in "The Seventh Victim," he just has to sit back and watch his creepy cult members do his killings for him. Pretty sweet gig, if you can get it.
Hjalmar Poelzig from "The Black Cat"
It's a rainy night, and Poelzig, played by Boris Karloff, allows a couple of strangers to enter his house for the night. But his motives are not pure: He's the leader of a Satanic cult and he wants to sacrifice one of them to The Man Downstairs. Luckily, a revenge-crazed Bela Lugosi is also involved, making this a kind of proto-"The Devil's Rejects."
Tommy from "Tommy"
Former deaf, dumb, and blind kid Tommy wants to show you the way to happiness. Unfortunately, that way mostly involves buying a bunch of stuff with Tommy's picture on it and spending even more money to go to Tommy's holiday camp. The actions of the cult in The Who's rock opera might not be as evil or murderous as some other cults, but they're undeniably crazy. And that's not even considering the whole swimming-in-chocolate-and-baked-beans-thing.
Mola Ram from "Indiana Jones and the Temple of Doom"
Just because a cult leader is well-organized doesn't mean he isn't crazy. Mola Ram specializes in leading hypnotized child slaves to work in his mine so he can dig up some magical rocks or something. It's an impressive operation, but pretty nuts, especially when you consider his penchant for ripping hearts out of the chests of his human sacrifices.
Kung from "Once Upon A Time in China II"
Ra's al Ghul from "Batman Begins"
Batman is there to stop him.