Batman is the Ace to such a degree that it's practically a super-power. He's the world's greatest detective, non-super-powered melee fighter, physicist, chemist, engineer, tactician, strategist, pilot, you name it. But it's balanced out by him having seriousissues. He also tends to lose badly when faced with a brand new adversary he's had no opportunity to study and prepare for.
In Boxers & Saints, Red Lantern Chu is considered to be this by all of the people in the village of Shan-Tung.
The reason for Solaris The Tyrant Sun's second FaceHeel Turn in DC One Million was that every single descendant of Superman proved far nobler than him, causing great jealousy on his part.
Herbie Popnecker (aka The Fat Fury), as a sort of comical early deconstruction of superheroes, would qualify as a preeminent example, though he doesn't look or act the part, and his parents are oblivious. Invincible, endlessly talented, loved and trusted by his allies, respected and feared by his enemies, irresistible to women (on one occasion, much to his chagrin), famous throughout the universe, there's simply nothing he can't do with ease.
Best Tiger of Guarding the Globe. The world's greatest marksman by a ridiculous margin, he wears a blindfold so his work won't be boring. He infiltrated a bunker that only Magnattack should have been able to access. He once incapacitated ten men with one bullet (and no, they weren't standing in a line). His Guardians of the Globe teammate Knockout thinks he really is blind, and that his kung fu is so good he can somehow pass for a seeing man, and he deduced that Outrun wasn't herself because he could hear the difference in how she shaves her armpits. As he puts it, they don't call him "Good Tiger" — he's the best. He is, however, antisocial in the extreme, and has no life outside of being Best Tiger. The Best Tiger is always hunting.
Hawkeye was this during the early run of West Coast Avengers. In a scene in which he's fighting to keep the Quinjet he's piloting from crashing, the narrator comments that many Avengers get praise for doing one thing well, but not Hawkeye—because he does MANY things well.
Kick-Ass is not one, but Justice Forever gladly accept his offer to join the team based on his reputation as one. Although he is one of the more competent and likely the most experienced heroes.
Lucky Luke might be the most notable example from Franco-Belgian comics. A "poor lonesome cowboy" and gunslinger with impossible aim and reflexes (he can draw faster than his own shadow, after all!), he's always in control and usually two steps ahead of everyone else. This is purely Played for Laughs.
Similar to his mentor, Nightwing, who is acknowledged as the world's greatest acrobat, the best leader in the DCU, to the point where villains will team up with him because he asked nicely. This is in addition to being an extremely skilled, non-super-powered melee fighter and detective. He's also considered one of the friendliest people around, and is shown to be on good terms with almost every superhero in the DCU. Within the Batfamily, he's also this, being the only person Bruce treats like an equal, the guy all other Robins have to live up to and the guy who made a better Batman (for Gotham, at least) than Bruce himself.
Steve Trevor is a high-flying, death-defying manly manbut unlike many other such characters, who are often womanizing pigs, he has the utmost respect for Wonder Woman and consistently defers to her.
Superman himself has to count sometimes too, especially in certain stories like Our Worlds at War which were seemingly written just to show how much better than every other superhero he is.
Tintin. He can knock out guys that are twice as big as him, drive motorcycles, planes, and tanks, survive gunshot wounds, and do a lot of other crazy stuff and still live on. And he is also really smart and very much a Nice Guy.
Hal Jordan of the Green Lantern series could be categorized as this, what with most other characters recognizing him as one of the greatest of his contemporaries.
The Transformers: More Than Meets the Eye set up the obscure character Thunderclash as this, in particular contrast to the Ragtag Bunch of Misfits that were the crew of the Lost Light, having met up with them after his ship was damaged "rescuing some orphans from an exploding sun". He even founded the Thunderclash School of Heroic Arts, the only confirmed graduate of which went on to be one of the most famous Autobot generals of his generation.
"You see, Thunderclash wasn't just a teacher, a trainer, a leader, a mentor, a role model, a counselor, a thinker, a sage, an idol and an inspiration — he was a friend."
This is itself a reference to Thunderclash's era (early-90s Euro-exclusive G1), where, for whatever reason, the toy bio writers seemed reluctant to give anyone a personality besides "ridiculously hypercompetent" or any tech spec stat below 7. Rotorstorm and Rapido have also been portrayed as this in their appearances since then (though the former is something of a Broken Ace).
Asterix is, despite his small size, the best warrior of the village. And he also happens to be one of the smartest characters in the whole series.
What happens when The Ace is a bad guy? Well, in that case you probably get Doctor Doom, who is: one of the Marvel Universe's greatest geniuses; an Omnidisciplinary Scientist who has done everything from curing diseases to building robots to creating fully functioning time machines; a sorcerer almost on par with Doctor Strange; the semi-benevolent dictator of a small Central European nation; the builder and wearer of a suit of armour to almost rival Iron Man's; a skilled musician and appreciator of the arts; and even when denied all of the above, he's still physically fit enough to kill lions with his bare hands.
Monstress has a backstory example in the Shaman Empress, who was apparently far and away the most powerful Arcanic ever. She was also a scientist of the highest calibre and developed technology and magic that Lady Yvette claims "...makes anything we have currently look like the Dark Ages." Unfortunately, the Shaman Empress took everything with her to the grave, and this has led to adventurers of all stripes looking for her tomb, including Maika's mother, Moriko Halfwolf.
The Transformers: Robots in Disguise: Prima is remembered by history (what little speaks of him) as the greatest of the Thirteen. Ultimately, this turns out to be a great big lie. Prima was actually not that great, and the one time he's shown fighting, it lasted as long as it took his enemy to cleave Prima in half with his own sword.