The only acceptable answers:
The Arbiter, Sgt. Foley, Spawn…
Fuck yeah.
BTW:
and a bonus:
https://www.bungie.net/images/games/marathon/wallpapers/VicOnARealBadDay_1600.jpg (too big to img)
The Postal Dude (Postal 1, 2 and III). Someone had to include the mad bastard at one point.
I can’t find a picture, but the dog from Jet Force Gemini is pretty awesome. Mostly because he gets outfitted with tank armor halfway through the game… but still awesome.
https://www.youtube.com/watch?v=V2Sf9bJzCiw
All my other, better ones have already been posted in some form or another.
Nah he’s not badass 
He is the most funny dude, i even seen.:jizz:
He tases people so they fall on the ground shivering, he bets of the head with a shovel, and then he PISSES ON IT.
Anyway, the most badass is:
Hell yeah, agent 47 with badass voice… actor.
Too bad the actor that played him in the movie looked like an up-and-coming 17 year old male model with a bald wig. Which MAY BE exactly what he was.
(these are in no set order)
- Kratos
2.The Strange
3.Big Daddy
4.Sephiroth
5.Rick
that last one, Rick, who the hell is he?
also
upon further analysis, big daddies become no big deal later into Bioshock.
it’s those damned ESP-endowed Big sisters you wanna steer clear of.
EDIT: Oops, posted as the database was going down, don’t know why it posted twice.
Yes Psyborg, we know.
I’ve seen the truth.
Ratchet. He’s badass.
He’s short, cuddly, and he can kill you in six different ways using a wrench.
(The fact he can carry that thing is also kickass 
It’s almost as long as he is!)
Long live Ratchet.
Are you kidding? That’s 3DRealms flagship from the early PC years, the other flagship being someone already been mentioned here.
THIS is COMMANDER KEEN!
…just noticed that.