Kendell Cambridge said:
The Boss. MGS 3. While it wasn't badass per se it was the only video game death that ever stuck with me, even years later
Got to be that. For all the complaints about convoluted storylines and such, Metal Gear games have always felt more emotional and deeper than other games, to me at least.
Not really sure if this counts, but one of my kings in Medieval: Total War II. I was playing as Denmark, and The Holy Roman Empire had basically dicked most of Europe, except for us. I was moving my King down to Hamburg alone with his bodyguard unit, and it's a two turn trip. So the Holy Roman Empire's massive army attacks, led by their emperor. Thanks to lots of my attacks and assassinations, he's their last male character over sixteen, so if we kill him the Empire is destroyed. And by lots of awesome, I managed to kill him with about 4 men left including my King, and then they were all massacred. It was awesome. Us and our allies took over the rebel regions and we all lived happily ever after (except France. We all ganged up on France).
Oh, and in the film of Sin City, Hartigan and Marv's deaths were incredibly badass. Hartigan in a selfless, heroic way and Marv's in an awesome tank way.