David 'Walky' Walkerton in It's Walky!; while part of his scatterbrained playfulness was due to brain damage and psychological manipulation, it was also at least partly intentional; at one point, Joyce points out that he had been an honors student in high school, which he immediately denies.
Depending on how one interprets his general tactics and his speech in the The Order of the Stick prequel book Start of Darkness to Redcloak after tricking the goblin into killing his own brother, Xykon also applies.
Xykon is more Competent But Lazy, he goofs off a lot of the time due to his arrogance, and incredible power level. He just takes advantage of people underestimating him when it occurs, often to do a little Hannibal Lecture here and there
When he first turns Xykon into a lich, Redcloak uses his holy symbol as Xykon's phylactery. He plans to use it to control him, and reasons that Xykon is too stupid to realize it. Then, when he threatens to destroy it, Xykon reveals that he knew about his plan all along, and that destroying his phylactery won't harm him unless his body is destroyed.
Right-Eye (Redcloak's brother) has a daring plan to kill Xykon for what he's doing to the goblins under his command. Redcloak kills him rather than let him destroy Xykon, since he needs Xykon for his plan to work. Then it turns out that Xykon knew about Right-Eye's plot, had a magic ring to protect himself from it, and didn't stop him before because he wanted to see if Redcloak was loyal enough to do it for him.
At the beginning of the comic Elan was genuinely stupid but over the years, perhaps as a result of (literally)gaining a level in badass and being Dangerously Genre Savvy Elan has become an actually valuable member of the team, though he sometimes still (likely mostly unintentionally) puts on a show of being quite bonkers.
He does have a fair number of bard levels... and bards, for all their flaws, has a couple of advantages in knowing stuff, even if their wisdom and, to a lesser degree, intelligence might be lacking.
Shojo. The man spent years pretending to be senile to trick his nobles into believing themselves to be competing Men Behind The Man so he could rule himself without fear of assassination.
Liquid Snake of The Last Days of Foxhound was initially a somewhat arguable case. It had been implied that despite his borderline idiotic behavior he was in reality a killing machine who has only been reduced to his current idiotic state because he suffered brain damage just before the start of the comic. Later it became less arguable as Liquid recovered somewhat and continued playing the dupe until he could attempt a revolt. Even towards the end of the comic he still falls short of his original portrayal in Metal Gear Solid, where he pulled this off quite well.
Helene from Avalon is a Clingy Jealous Girl, seemingly oblivious to the fact that her boyfriend, Alan, just wants to get rid of her (not to mention his interest in Ceilidh). In one of the last drawn strips, she tells Joe that she's known Alan's feelings the whole time, but the fact that he hasn't told her makes her think that he cares about her enough to be won over, and after being forced to admit this, gives up on him.
The interpretation of madness given in Narbonic explores this trope at length.
And this makes one wonder about Red Mage, and thesethreemake one wonder about Fighter. Of course, actually being as dumb as Fighter would be a far greater feat than pretending to be that dumb.
The second possibly shows a variant of this - he's not as dumb as he appears to be, he just never feels the need to actually think about anything beyond his whimsical Cloudcuckoolander ideas, one of which, remember, worked like a charm ("Sword-chucks, yo!"). A fighter actually using his brain is a threat to be feared.
The possibility of Fighter pretending to be dumb is lampshaded in this strip.
Red Mage is well...a Red Mage (third highest Int stat in the first Final Fantasy game), but he is too much an eccentric, stat obsessed, narcissist to concentrate on doing anything remotely competent for a prolonged period of time.
Bun-Bun wonders whether Torg is using this tactic or not in thisSluggy Freelance strip.
Well, seeing as Bun-Bun is saying "Break" and not "Brake"...
Master Payne: You cannot possibly be as stupid as you act.
Oggie: ...Ken if I vants to be!
Another example can be seenhere. Announcing your presence with a loud fanfare and a Slow, Badass March is of questionable intelligence in a world were massive death rays abound. Using said march to distract the enemy soldiers from the fact that most of the horde is already in the city and wreaking havoc...
Tarvek: What? No! That was that idiot from the Island of th...(makes a bug-eyed face) She is good.
The best thing is, in those two strips, she first confesses to using Obfuscating Stupidity, then she fools the man she confessed it to.
It gets better. She outsmarted Lucrezia. No, really. Zola is the Queen of this trope.
Well, it's more accurate to say she's one of the few examples of multilayer obfuscating stupidity. Initially the stupidity she was feigning was pretty obvious in it's fakeness, but then she dropped into a much more natural seeming smart but rather gullible act and it was only when she went up against Lucrezia that she finally dropped all the acts and revealed just how much cunning and treachery she had been hiding.
Baron Wulfenbach, however unexpected. He's clearly in fever. The moment a fresh minstrel from the street is in his room, Klaus knocks it off and express-interrogates the guy.
The Adventures of Dr. McNinja: Doc's younger brother Sean "Dark Smoke Puncher" McNinja, who is a bona fide Gadgeteer Genius and all-round geek but hides it behind over-the-top hip-hop affectations, since his parents don't want a secondBadass Bookworm in the family
This strip of Darths & Droids reveals that Jim, the rather dim-witted player doing Qui-Gon Jinn, is in fact studying geophysics. He acts as stupid as he does roleplaying because he uses it as downtime and turns off his brain.
Penny of Penny and Aggie, as the comic's Alpha Bitch, often acts ditzy in front of others. (She tells her friends, for example, that math is "fundamental" because one day you might find yourself stranded on an island "with a bunch of numbers that don't mean anything.") However, she's one of the school's top scorers on the practice SAT.
Cyndi, particularly during "The Popsicle War," acts like a celebrity-obsessed airhead to conceal her Manipulative Bastard nature.
Felicia in Ozy And Millie is shown to be quite smart, despite trying to act dumb to be with the "in crowd".
Avery also fits this trope, as demonstrated when he showed insight into Thomas More's Utopia.
In the "Tumbledowns" story in Tales of the Questor, Guardsman Mulharney seems a hardass constantly on Quentyn's case while he's going undercover to recover his stolen sword to the point where the young Questor was forced to physically attack him to maintain his quest. However at the end of the story, Mulharney admitted that he knew who Quentyn and correctly guessed he was doing something important from the start. Therefore, he played dumb to give the kid street cred to accomplish whatever he was attempting against the street gangs he was infiltrating.
Buck Godot has a rather shocking case of this in the person of the Winslow, as revealed at the end of the Gallimaufry storyline.
Looking for Group has Richard. He may seem like the insane character foil of Cale, but it's been revealed that he's really much smarter (and maybe less insane) as we've been led to believe. I mean, he figured out that his rabbit was the Archmage, something nobody could have guessed and he's apparently been following Cale since the very beginning, not because of boredom, but because he knows the guy is going to become something big..
For example, he is the mayor of a small village, which got under siege at one point. He askes his second hand if they "launched all the women and children at them." with catapults, to which he replies that they did but it didn´t have any effect. That plan seems typical Richard, nonsensical voilence and all and disregard for human life. But if you find out that the entirety of the village is undead, the plan makes a whole lot more sense and actually works out in the end.
In Bob and George, Mega Man, despite being a genuine idiot, is a tactical genius in battle. He even used his stupidity to distract Ring Man long enough for Mega Man to charge up his next attack.
He is, in fact, programmed for this. His primary objective is to "Defeat Wily and the robot masters", and his secondary objective is to "be an idiot". Guess which one takes precedence in a fight?
As it turns out, Dominic Deegan's father Donovan has been able to speak Orcish perfectly for the past twenty years. He's been mangling it the whole time simply because it was Funny.
Guineas from El Goonish Shive, a bit shy and lazy guy whose boss gave him only simple work because he avoided assuming his human form and acted as barely more than a dumb rodent. He isn't stupid.
This trope appears to be not only Blade Bunny's M.O., but her whole way of life. The first time the mask slips she glues it back in place by seeming unable to count to four.
Although, thus far, it's not yet clear to what degree it's this trope, and to what degree she's a genuine Genius Ditz or Bunny-Ears Lawyer with a specialty in being a ninja — she drops the "mask" so rarely, even when it's counter-productive, that it could be either or some of both.
Yuffie admits to doing this in Ansem Retort, pretending her English skills aren't as good as they are because it makes it easier to rob people. And fools people into thinking she knows kung fu.
Sgt. Schlock of Schlock Mercenary behaves in a childish, innocent manner and doesn't seem to deeply understand anything...but is actually far more canny and observant than this suggests. This may not be an example, though, as it's unclear to what degree, if any, he intentionally cultivates this rather than it just being how he is.
Gabe from Penny Arcade. Despite his antics and general naivete, he lets on that he may be smarter than most people think. He just spent years of his life faking stupidity so that his parents would stop calling and asking how to fix their computer.
Grymm from Voodoo Walrus seems to be playing at this since he always seems to be lost in a haze of obliviousness, and yet he can still step up and solve problems when least expected and pull part time duty as a self-centered, greedy, manipulative superhero.
Except that recently there's been evidence to suggest that Grymm and the masked T-Square couldn't possibly be the same person.
The Trenches: After being turned away by multiple potential employers for being "overqualified", Isaac resorts to this.
Isaac: Use small words, Isaac. Use small words...
The governor of Beldatz in Nahast: Lands of Strife. Considering that there is a legendary organization of spies watching his every move - directed at least in part by his wife, no less - it's quite impressive that he manages to maintain the deception. Additionally, his daughter is part of the organization watching him.
