hmmm... we have a stellar crew:
Human: Arthas (then Kel'thuzzad)
Orc: Gul'dan (then Garrosh)
Draenei: Kil'jaeden (then Archimonde)
Thalassian Elf: Sylvanas (then Dark'han)
Night Elf: Azshara (then Xavius)
Worgen: none
Forsaken: Putris
Tauren: Magatha Grimtotem
Dwarf: King Thaurissian
Gnome: King Mechagon
Goblin: Gallywix
Panda:
Troll: Prophet Zul
Interesting how several horde leaders actually make the list of most evil of race. However, it's the so called pretty/good races that are typically famous for virtue that have the most evil race members. (