CarolinaPaddler:
Truly in my mind one of the most iconic anti-hero's of cartoon lore was the Joker in the Batman Movie. I could easily picture him putting Bat Girl over his knee and cackling with that special laugh as he spanked he leather panty-clad bottom.
Well, that's a fun fantasy for many spankophiles (although I'd be hoping for Batgirl's 'bat-panties' to be lowered at some point), yet as he's generally been portrayed (comics, television and movies), I would hardly consider the Joker to be anything but a villain--sure he's got some degree of style and a bizarrely ironic sense of humor, but the guy is basically a homicidal maniac.
Now Magneto, he's an antihero, I'd venture that there's no serious doubt about that--sometimes he even ends up fighting on the side of Charles Xavier (who addresses him as "old friend") and the X-Men, although he doesn't share Professor Xavier's approach to defending mutantkind.
As to the issue of the spanker's role in a spanking-oriented account, well depending on his/her motivation for administering corporal correction, I'd say that he/she could be hero, antihero or villain, using the term in a broad sense.
Hero/Heroine: The discipline is believed to be clearly deserved, and is delivered at least partially for the spankee's long-term benefit (even if the spanker does get some personal satisfaction from it).
Antihero/Antiheroine: The punishment is administered as part of his/her responsibility, he/she believes that it's justified under some set of rules, but his/her personal emotional involvement is somewhat limited.
Villain/Villainess: The chastisement is applied to the posterior of an innocent victim, one whom the spanker knows is innocent (or possibly he/she doesn't care whether or not the spankee is guilty), the spanker getting a great deal of personal gratification from his/her role.
Obviously, these descriptions are referring to the spanker administering a butt-blistering which the spankee at least consciously would prefer to avoid (even if he/she admits to needing and/or deserving it), of course erotic spanking play is something quite different.
That's my thinking anyway...

--C.K.