He killed his own brother in a cruel way :S

Jafar becuase his plan didn't work at first but he came up with another one that almost worked

Actually I recan that evil Scar is the most king but he's not he being cruel killing his own brother Mafassa that's a bad way to do. But only Simba is a king cause he's my favourite he's most brilliant king at ever all just cool!

I guess Frollo.

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But where is the Coachman? He kidnapped children, turned them into Donkeys, and basically made them slaves that is terrifying.