As much as I didn't care for the later movies, I would have to say "Mr. Jigsaw" himself. Because this man was a sadist even in death and he influenced others to become sadists as well! I included the pic of the puppet because it's just creepy...
@gothic_storm: YES! John Kramer is awesome.
Also the main Nazi from Inglourious Basterds, that guy was so creepy. I'm sure there are more, I just can't think of anymore off hand.
EDIT: Yes, both of the guys from the Human Centipede movies. Those movies are just too much... lol (In a good way) Such good creeps though. I feel the need to verify that I'm not a pervert/sadist, I just think the movies are so intriguing in a strange, weird way.
EDIT 2: @nerx, now I really want to see that based just on the GIF alone... :-/
@the_stegman: DeLArge, uses a porcelain prick to kill an aunt
@omgomgwtfwtf: Mads Mikkelsen is one badass dude, mah nyugguh
Kakihara is a masochist really, hence why he wants to find Ichi but kudos for liking Mike's rendition of Koroshiya :)
Others I like
Vukmir and his immortal words
real men wear fat women :3
@omgomgwtfwtf: Hes more of an S&M guy, does not specialize and when comparing human to non-humans I automatically give the non human a minus on the fact that they have it more easy.
For example take this leader from 'Martyrs' no super powers but they have dome pretty much every horrible act to women
Drayton Sawyer (Texas Chainsaw Massacre 1/2)
Nubbins Sawyer (Texas Chainsaw Massacre)
Chop Top (Texas Chainsaw Massacre 2)
Of course Leatherface (if you can call him a sadist guess it depends)
Freddy Krueger (A Nightmare on Elm Street series)
There are more but that is it for now...