[Shaun]

hmmm. In terms of all-out badassery, rather than perhaps the most evil...

1) Darth Vader obviously
2) John Doe, Se7en
3) Elle Driver, Kill Bill Vol. 1 & 2
4) Li'l Ze, City of God
5) T-1000, Terminator 2: Judgment Day
6) Scar, the Lion King
7) Chancellor Adam Sutler, V For Vendetta
8) Kevin Katchadourian, We Need to Talk about Kevin
9) Hans Landa, Inglourious Basterds (just for the opening scene)
10) Cruella de Vil, 101 Dalmatians (either animated or otherwise)