Mister Spock. The second ultimate Mary Sue next to Superman.
Whoa whoa whoa, hold on there. WOLVERINE is the biggest Mary Sue, alongside BATMAN, and possibly the Punisher.
Actually, I don't know if *biggest* is the right word, as being a Mary Sue is a state of invulnerability beyond the legitimate bounds of one's powers; and based upon popularity.
Superman is simply acting within the structure of his stated powers and concept. He has a wide array of powers, or rather a range of things his powers can accomplish: super speed + flying + super strength is a really awesome combination. Add to that the heat vision, X-ray vision, and microscopic vision and you've covered a lot of exposition points, sure.
I would counter, however, that he has so many specific and known weaknesses that get taken advantage of regularly; and that exposition principle "show how dangerous the bad guy is by taking out Superman" is enough that he's been defeated many times. Indeed, he needs to be defeated, weakened, etc. simply to show off other characters around him.
(other examples: Thor, the Sentinel, Galactus. None of them should lose *ever* but they do so people can see how amazing the new threat is, or how Mary Sue the protagonist in the story is)
On the other hand, Batman has no powers except his training and gadgets, and yet he *never loses*. The point is that he SHOULD lose, and so he NEVER loses. He shouldn't be able to take out Superwoman, or Superman, or survive against Darkseid AND YET HE DOES. The drama for him is that we've established his vulnerability by his very concept, and yet we never actualize that vulnerability.
Wolverine is similar, except that his powers compensate for things they shouldn't. He has undergone a massive power surge since I was a kid. In fact, he's gotten taller, too. He can regenerate anything, so no poison can harm him, nor disease, and even being reduced to a skeleton doesn't work.
This was not the case earlier, when he was a minor-if-popular member of the X-men, a minor team in Marvel. He was a short, surly alcoholic who smoked too much, and lusted after another man's girlfriend *unsuccessfully*. He was hairy, and mean, and had a low charisma to say the least.
Now he's this paragon, has two spin-off versions of himself, and a backstory. A Backstory?! Wolverine *should not* have an origin story beyond waking up in Weapon X!!!! No excuse, I say!
The only reason for all of this: he's popular, so he can't lose.
The Punisher: He's popular, and so he can break into the Baxter Building during Civil War? Um, no? He's a human with no powers, vs. the intellect of Mr. Fantastic. (another example of someone every new comer has to out-wit in order to be considered smart. He's supposed to be the smartest!!)
Deadpool: another example. Maybe the reason I find this hard to stomach is that he was made up by Rob Liefield... (cough, just kidding; good job on that one, just being sour here). Okay, the real reason is that he gets away with a lot due to the healing factor and enjoying killing stuff, and he's funny. He's great in Hulk vs. Wolverine (good cartoon), but now he's got the Deadpool Corps? They need to die in a fire.
Being Mary Sue means never losing, sure. However, the reason for never losing is because that's their trait: They don't lose. There's no back up reason for it, like being a Kryptonian powered by the yellow sun of Earth. They may have "mad skillz", but so do their opposition; and often more so. Rather, they win because, simply: I'm Wolverine/Batman/the Punisher/Deadpool.
Final example: Drizzt. Stats-wise, he's never as powerful as he should be. Yet in the books he never loses. Back in the 90s he had 13 Str, but could always one-hit-kill. That didn't really change even in 3e, where most PCs of his power level were multiples of damage output over him (twf vs. power attack at high levels?); and nowhere near enough magic gear to warrant survival against a marilith or other critters (ie: what's protecting him from saving throws, other than his raw ability score modifiers?)
Most of the adventures up to the Orcs books, he was fighting fairly low level critters (orcs, giants, etc.). Yet he took on several high level drow matrons/clerics in one book; and this was waaaay before 4e.
And why is he so much higher level than the rest of his party? Like Cattie Brie is 4th level and he's 15th? Even Wulfgar and Bruenor are only 10th. Well, they're all dead now, so that wraps that up.
Oh well. You get what I'm saying. Can't lose!