Who is Vizzini from The Princess Bride and what is their importance?

Vizzini is Sicilian with a angelic face that belies his sly demeanor. Vizzini has a humpback due to having one leg shorter than the other, but is very quick for his deformity. Vizzini is a brilliant mastermind who enjoys torturing others. Vizzini is hired by Humperdinck to kidnap Buttercup and stage a war between Florin and Guilder.