Yeah, if you want to find more characters like this I'd suggest looking at the tropes, and sub-pages of, Anti-Hero and Well Intentioned Extremist, maybe even Anti-Villain depending on your point of view.

Also, while it's not quite what you've asked for, there are a number of times where actual villains have teamed up with the heroes of a series in order to take down a worse villain. See Rivals Team Up, Enemy Mine and Teeth Clenched Teamwork for examples of that kind of thing.

The few characters that immediately sprang to my mind were:
Sergeant Schlock, from the webcomic Schlock Mercenary (and, to a lesser extent, the rest of Tagon's Toughs). On the 'hero' side, they have saved people, planets and even had a hand in saving the galaxy one time. On the 'less-heroic' side, they usually only do that stuff because they're getting paid for it, frequently use violence as a first resort, and aren't always that concerned about collateral damage.

Their skills can generally be summed up as 'breaking people and hurting things' (or maybe the other way around), and most of them enjoy the pretty lights caused by massive explosions.

Having said that, some of them have managed some truly heroic feats when their friends were in danger. Other than that, they can be heroic, but usually only if they're getting paid to be heroic. Tagon's priorities are 1) survive in order to get paid, 2) get paid, 3) client satisfaction.

Belkar Bitterleaf, from the webcomic Order of the Stick. He is a member of an adventuring party that is one of the few groups actively trying to save the world from impending doom, but his alignment is Chaotic Evil. For the most part, he only really cares about himself (and, later on, his cat) and occasionally suggests plans for dealing with obstacles/distractions which are very efficient, but morally wrong. The rest of the party tends to stop him from actually acting on his villainous impulses though.

Amanda Waller, from the DC universe. She runs Task Force X, a.k.a. the Suicide Squad - a group of not-even-slightly-reformed supervillains that she (barely) keeps in control through the use of explosive collars.

The Squad only tends to get used against targets that are even worse than normal, or in situations where sending regular forces would just be sending them to their deaths, so she does do good, but her actions are completely illegal and immoral.

- Irish

You can count any player character who can potentially act evil, even if it's not necessarily the 'canon' route. Let's take The Lone Wanderer, from Fallout 3. Essentially the chosen one in all but name, you can save the day, even if you sell fifty people into slavery, murder your way across the wastes, peddle more drugs than the Los Zetas, or just kill people so you can eat them. Sounds pretty villainous, no? The weird part is that you can just go donate a bunch of caps to a church and you'll still get the title 'Earthly Angel' or something even better sounding.

I'm not completely sure what you're asking, but it seems like you want to know if the narrative role of 'the hero' has ever been given to a far less savoury type. I've answered according to that.

... practically the definition of 'antihero'?

hS

Is this what you're looking for?