Your favorite badass game vilain/hero?

Mr. Salieri (Mafia)

Makarov

Reapers from Mass Effects

I can't decide between Dante and Vergil (devil may cry). Dante is badass, Vergil...he's just plain cool.

War from Darksiders, because at one point he rides his burning horse away from a giant sand worm while shooting it with a magic gun.

Oh, or this guy: http://www.youtube.com/watch?v=i5JlvAwE510

Julie from Heavy Metal F.A.K.K. 2

nsfw, js

Spider Jerusalem

Villains:

Reapers (ME)

Irenicus (BG2)

Kerghan (Arcanum) - my absolute favorite, he's about the only villain that had a logical reason to be one.

GLADoS (Portal)

Bit of a special mention would be Ravel from Planescape. Not to spoil anything, but i can't help but feel sympathy for her.

Hero:

Shepard (ME; Because i can go Mary Sue)

Jensen (DX3)

The Tuurngait

G-man

Duke Nukem

Serious Sam

Villain - Makarov from MW
Hero - Ezio Auditore

Spawn

Caleb, from Blood 1.

I still love good old spartan-117

Zetta, from Makai Kingdom.

The antagonist from Pokemon blue/red/yellow/.../ who is always one goddamn step ahead of you or the final boss of Super Smash Brothers (the hand).

Most badass hero? Every hero, cause I control them.

;)?

I'm shocked if not disappointed that The Jackal from Farcry 2 hasn't made this list yet. If you listen to the tapes etc. you realize how well written the game (despite being super-sandbox) really is.

Yogg Saron, and to a lesser extent C'thun from World of Warcraft. (Also worth mentioning Illidan probably. Didn't care for Arthas I think he was too late to that archetype to be interesting.)

Andrew Ryan from Bioshock has to be worth at least mentioning. Frankly, a lot of the characters from the universe probably fit on lists similar to these for one reason or another.

Prophet from Crysis/Crysis 2 (You can include the character swap if you want, I personally don't though.) Very well done rationalization and humanization of the weaponized soldier type.

Geralt from the Witcher series really should have shown up by now on this list somewhere. The good ole' monster hunting monsters with mixed feelings from the civilization/societies around him/her has been done a lot, but the quality of delivery was wonderful.

As for names already on the list -
I'm not a huge fan of Makarov. He has some interesting lines to deliver, but wasn't very well developed and/or felt very generic. He talks about how meaningless power is, but then spends the whole series seeking it.

Jackie Estacado - based on just the trailer of The Darkness 2 seems rather amazing as a character, but I have to admit I haven't played either game.

War from Darksiders is great as well, although it almost feels like he loses depth as the game goes on. Nothing wrong with a whip and pistol wielding horseman of the apocalypse riding a fiery steed and slinging a car sized sword on his back tearing through countless demons and angels seeking absolution for something that wasn't his fault. None of that romantic interest BS either. A mans-man. A demons-man?

snake

Dark Queen from Nes Game BattleToads

Sly from the Sly Cooper Series.

A.K.A. "The Maked one" (S.T.A.L.K.E.R. SoC) http://stalker.wikia.com/wiki/Strelok

Villain : GlaDoS

Hero: Ratchet (Ratchet & Clank)

Kreia from KOTOR2 is by far the best...
(and also the only character in that game with any real depth and development :P)

Just for badass-ness, it must be Kratos, from God of War.

Guts (Yeah it's not from a game but he is too badass to care about that)