I figured this would be a fun exercise. Who in all of gaming has the highest kill count bar none?

I would give it to Samus for the following:

May be some potential spoilers for the Metroid games.

All the characters from Dynasty Warriors....

Frank West.

Mario

He's asking for one, so I'd say Lu Bu, specifically.

Samus may have more kill count... but Dynasty Warriors wins in terms of humans, I believe.
The carnage Lu Bu leaves behind in one single game of Dinasty Warriors (especially if you want to upgrade his stats) is staggering. I'm sure I've killed more than 20000 people with him in my DW4: Extreme Legends game.

The guy from Crimson Land:



And that was just one of many many levels.

Any character fighting random battles on an RPGM3 field map set to "low" encounters.

^ Oh, SNAP!

I never played it to the end, but didn't an entire universe get scrapped at the end of Chrono Cross? It seems like the thing that'd happen in the end of that game.

Definately Mario. He's starred in something like ten platformers. Mario 3 in particular, he would stand around as a shell bounced around below him while spinies rained down, all in an effort to aquire 99 lives. There's also the five or six RPGs, and that's a lot of enemies that he kills just by rule of RPGs (even though they respawn when you leave the area). And if we include the dozen of Mario World hacks that exist, that's even more enemies killed. Let's face it, the Mario universe is a battle zone.

Oh yeah, and also: Dr. Mario.

Anyone actually play through Heavenly Sword?

You are required, by the game, to kill 700 soldiers before you can proceed with the story... in more than one place.

And not only that, at the tail end of the game, you can do this:
(Major spoiler warning, though it's PS3 exclusive and seeing there's like only 2 other people besides me with one of those, you should be fine.)

Foot soldier.

The FFX cast.

Each monster they defeat is made of many souls of people. And bosses are made out of a crapload of souls.
They put to rest more than half of Spira.

Yeah, but at least that was more of the good deed of exorcising the restless dead rather than killing. ^_^

What about Leon? He probably has his face on a wanted poster on every corner in Spain after the events of RE4 (OMG! Resident 4 is racist, too! I just realized it!)

You have no reason to believe that was Spain, mate. They never said anything in the game.

Meh, it's probably Ryu. Hadouken has a bigger kill count than anything out there.