Silly Hats said:
Seriously? No Hiro Protagonist?
He even has "Last of the freelance hackers and Greatest swordfighter in the world" on his business card
I figure most people here are too young to have actually read most classic dark future fiction like "Snow Crash", it's just not really current or geek-chic anymore, though people will sometimes pretend to be familiar with genere classics.
To be brutally honest the very nature of this competition prevents any serious discussion since probably nine tenths of the characters suggested are pretty much disqualified automatically for inherently tapping into superhuman abilities, even if it's loosely defined "Chi" or whatever as part of their skill.
My answer however would be Benedict Of Amber, from Roger Zelazny's "Amber" books. The basic concept is that there are only two things in the universe which are "real" the formlessness of chaos, and the pattern or "form" of Amber. The rest of the multiverse including all other dimensions are simply shadows cast by the contrast of the two, many believe themselves to be the center of the universe, or the true reality, but it's not true... yadda, yadda. Ultimatly even if quite different most people and beings of note are simply reflections of beings of note in the true realities. Benedict Of Amber is pretty much *THE* ultimate fighter in the entirety of creation, other invincible seeming fighters tend to be reflections of him or the other princes and princesses (sometimes each having what amount to multiple reflectios in a given reality) but as the undisputed best of the bunch a reflection of Benedict is pretty much going to be a better than a reflection of anyone else, and when it comes to a straight fight Benedict is undisputably the best of the Lords Of Amber. The reason I mention him is because this is about raw skill, as opposed to bringing in any other kinds of powers like mastery of magic, manipulation of shadows (ie reality alteration), trumps, or what kind of other resources he might have to draw on, as he can be (and is) overcome by others, but he is conceptually the most skillful fighter in all of reality, his skill being mirrored across the entirety of creation. One recurring question in the stories is who the second best fighter in Amber is Eric, Corwin, and Bleys all wind up crossing blades trying to figure this out, arguably it turns out to be Corwin which makes him #2 in all of reality but when it comes to being forced to cross blades with Benedict he knows he has no chance, and typically winds up having to run away and find conditions where he can resolve
a fight outside of the realm of pure martial talent.
Of course this is very much a series/universe specific concept, which winds up pretty much defining anyone else you can think of as being an "imperfect shadow" at the very best, at the end of the day, especially when getting to shadows cast very far away from the true reality, most people and things won't have the "honor" of being anything close to a proper reflection... it would take a long time to explain how that all breaks down and all the permutations of it though. But basically if you bring up Benedict of Amber, he wins... period, as the concept is simply that he is the ultimate fighter in all of creation.
To get a little less obtuse, I'd probably nominate Lancelot as a conceptual runner up. A real classic there. Lancelot is pretty much defined as being invincible on terms of skill alone. Depending on the version of the story, you even run into cases where Lancelot is pretty much volunteering for suicide missions to get himself killed off out of shame for his love of the queen, and keeps failing because his honor as a knight demands that he really try and win, and he literally scours the earth picking fights with the nastiest no-win scenarios possible and literally nothing can beat him because he's just too bloody good. The versions that define him this way the whole "Ill Made Knight" concept popularized by parts of "The Once And Future King" and then run with, typically gloss over the specifics, but he's more or less supposed to be pretty much single handedly throwing himself against the best forces of Asia, The Middle East, Europe, and anywhere else, huge monsters, etc... and always goes it alone forgoing help from other knights because he secretly wants to die. Typically the only fight Lancelot tends to "lose" is against Galahad, and that usually comes about due to divine punishment for Lancelot's betrayal of the king, with God pretty much directly smacking Lancelot down through Galahad. Of course Lance typically gets his mojo back and shows up to pretty much single handedly save the day for the rest of the kingdom in the final act... where "the rest of the kingdom" is key since Arthur usually bites it in one spectacular way or another in the same battle and is taken away through the mists.