The Lady Knight in Child of the Storm, a human woman (albeit immortal) who hasn't appeared on screen, but has cast a shadow over proceedings. She taught most of the major badasses in history how to fight. Cuchulainn? Taught him. The Argonauts? Taught most of them. Real Life badass William Marshal, the greatest knight? Taught him too. She even took Sif and Fandral under her wing and turned them into the Goddess of War and the finest swordsman in the Nine Realms with only Sif for a peer respectively. She was also the best of Arthur's court: yes, even better than Lancelot. No one really knows anything about her, beyond the fact that she's epically badass, trapped on The Slow Path (save for intermittent time jumps) and probably something of a Hurting Hero by now - though she hasn't been seen since the 18th century.
And more prominently, the Winter Soldier. Pretty much the entire cast, both good and evil, is either starkly terrified of him, or, at the very least, regards him with a kind of wary respect. Pretty much every time he makes an appearance, he very much lives up to his rep.
Doctor Stephen Strange. Lots of characters in various media are either The Archmage or a Magnificent Bastard. Strange is both. He plays every single character in the series like a harp, with the exception of Sinister, because the latter is blocked from Strange's foresight, and even he can only do so much with the Endless - though he still seems to be able to get them to do pretty much what he wants. He even gets a mention in the House of Magic and is an accredited member of the Omniscient Council of Vagueness. Oh, and he's a time traveller.
On the occasions when he gets his hands dirty, well, he dueled a Physical God Dark Wizard to a standstill and walked away whistling, and defeated a Physical God-level Humanoid Abominationwhile multitasking. This, by the way, is on top of his normal job as Sorcerer Supreme, which job description basically entails scamming and/or beating up Eldritch Abominations.
He also (see below) resurrected Harry Dresden, with the person in question later making it clear just how impressive this was. Resurrecting someone as a zombie is one thing. Grabbing someone's spirit and putting it back in their body so that they come back exactly the same as before? That takes incredible skill.
Harry Dresden, as per canon (see the Literature page), whose reputation is given a spectacular boost after his duel with Gravemoss under Paris, which ended with Dresden unleashing his Death Curse in the form of a vast column of flame that jetted over a thousand feet into the air and launched Gravemoss from under to Paris to the North Sea, several hundred miles away. And, impossibly, he survived (well, to be exact, Strange saved him). While Dresden sees himself as more of a Badass on Paper, discussing the trope in his internal monologue, his rematch with Gravemoss during the Battle of London, which was caught on camera, and resulted in Dresden forcing Gravemoss - who is in the same weight class as freaking Loki - to run for his life, only burnishes that reputation. Oh, and he's in line to be Sorcerer Supreme one day, meaning that many feats of Memetic Badassery are yet to come.
Harry Potter/Thorson, meanwhile, has a rapidly growing reputation, partly because he is the Boy Who Lived, and partly because he is the Boy Who Continues To Live No Matter What Is Thrown At Him - no matter whether he's being attacked by Death Eaters, Basilisks, Dementors, Voldemort, the Disir, the Slendermen and HYDRA's Werewolves, Project Ultimatum, Daken, armies of HYDRA troops both muggle and magical, Gravemoss, the Elder God Chthon, Voldemort again, the Death Eaters again, Sinister, Dudley a.k.a. the Blob/the Beast, Maddie Pryor/Rachel Grey, the Red Room, Dracula and the Grey Court... one way or another, no matter how outclassed or outmatched he is, he'll come out the other side intact - and increasingly on top, as he gets stronger, more skilled and savvier. Which is generally more than can be said for whoever's gone up against him. Or whatever's left of them, anyway. After the incident with the Red Room, Draco Malfoy, who's been quietly, and with reasonable accuracy under the circumstances, deducing what's happened, flatly states that there are very few organisations he can think of capable of containing Harry, and they're mostly supernatural superpowers. And none of that takes into account the Phoenix.
Mr. Black in Make a Wish. "Whoever caught the rabbit first would get the title of the best and be given the job of tracking down all the death munchers. Umbitch took one look at the forest and concluded that rabbits don't exist. The Aurors went in with fifty men and came out with ten . . . having fought a great battle with the rabbit and barely escaped with their lives. And Mr. Black . . . he didn't even bother to show up . . . three days later, the rabbit died . . . of 'natural causes.'"
Don't you mean that the rabbit died . . . in an 'accident'"
"Yeah! Twilight Sparkle!" The gryphon went on, oblivious to Twilight's nervousness and Pinkie's Pinkieness. "She's an alicorn sorceress from Manehattan. Purple, kinda like you." The large gryphon leaned her head down and lowered her voice, conspiratorially. "Rumor going around the aeries is that she's actually another sister of Celestia and Luna and the Manehattan story is just a cover. You really didn't know about this?"