Steve's friend Barry from American Dad! he is generally seen as a very unintelligent individual. But in some episodes he is shown to be very good with mechanics; when asked about this, he replies that he doesn't know how he did it. Another episode reveals that he isn't as stupid as he seems: he is actually a very intelligent psychopath who takes pills to control this side of him.
It's very difficult to tell, so sometimes one also wonders whether Francine shows this; she's often shown giving basic answers to complicated issues and spouting non sequiturs at the most inappropriate moments, but she's also shown signs of brilliance; she's a natural at pretty much any form of business, and has almost always been right in arguments against Stan, although that isn't really saying much. She did, however, lead an entire handicapped mafia to their deaths.
In the Disney cartoon American Dragon: Jake Long, there is Spud (an apt name, considering his displayed personality). Spud has the personality of your average idiot (and sometimes worse), but once, when tricked into doing an aptitude test, he gets a perfect score and is sent to a school for geniuses, where he also is far smarter than any of those people too. Spud explains that he does so because he doesn't want the pressure of having to perform to live up to the expectations others might have toward a young genius. He'd rather enjoy life as an easy-going goof.
It's unknown exactly which parts of Bumi's behavior are Obfuscating Stupidity and which (if any, or all) are genuine weirdness. The only thing we do know is there's enough Obfuscating Stupidity for him to really be a ripped and awesome earthbender.
Iroh, top to bottom. Looking at the polite old man, you'd never imagine he'd once held the last bastion of resistance to the fire nation in slowly constricting grip. Almost everything he says in adverse situations is well-obfuscated, extremely polite deadpan snark. Also, when he was imprisoned in Book Three, he pretended to be insane while secretly doing exercises in his cell so that, after a while, all of his fat appears to have been replaced with sheer badass muscle.
Harleen Quinzel may seem to be just another dumb blonde, but before she embarked on a life of crime, she was a psychiatrist at Arkham Asylum. The few times she's not speaking "in character," she speaks with what is arguably a refined English accent, suggesting that she came from "good breeding." Among other things she's done that suggest that she's smarter than your average bear, she has gone toe to toe with Mercy, Lex Luthor's highly trained bodyguard/personal assassin, in hand-to-hand combat on repeated occasions, eventually coming out ahead (well, Quinn was able to walk away, even in handcuffs, Mercy wound up in a hospital bed). She also, upon seeing that Joker was really depressed on one occasion, came up with a plan to capture Batman, and then go that extra mile and actually successfully execute it so effectively that Batman's only way out was to exploit Harley's and the Joker's psychological issues. Harley does still have her eccentricities though, and it can be hard to deduce just how smart (or dumb, or insane) she really is. She summed it up best herself:
Harley: Betcha thought I was just another dumb blonde, huh? Well, joke's on you! I ain't even a real blonde!
It is implied in Ben 10: Ultimate Alien that the titular character was doing this to some extent throughout the original series in order to cope with suddenly having to deal with interstellar and supernatural threats on a daily basis as a ten year old boy.
Bobby's World played with this from time to time. While Bobby was, for the most part, genuinely naive, there were times when he would overplay it to cause problems for Derek or Kelly, while appearing innocent. One notable example was when he repeated everything Kelly had said about her ex-boyfriend (who she still liked), in front of said ex-boyfriend (who had come to apologize after their fight), while pretending to not know what it meant (needless to say, he ceased to be apologetic).
This was Bugs Bunny's strategy in Barbary Coast Bunny. After Nasty Canasta stole his gold, Bugs the Karmic Trickster pretends to be a hopelessly naive hayseed during his visit to Canasta's casino. He promptly bankrupts it by effortlessly winning big at every game of chance.
Clam from Camp Lazlo is a Cloud Cuckoo Lander complete with Simpleton Voice, but starting with Season 1's "Prodigious Clamus" and onward, this trope has become one of his primary character traits. To elaborate, he paints a perfect replica of the Mona Lisa in a matter of seconds and plays an entire symphony by blowing a bottle in the aforementioned episode. In another episode, he builds an enormous, perfectly functioning segway-like vehicle from a massive tree trunk complete with steering handles in a few minutes.
Quinn Morgendorffer (Daria) is a canonical example of the fake-ditz variant. However, it is implied through the series that she hid her intelligence even from herself, for fear of emulating her perpetually unpopular yet brilliant sister Daria.
Doug: Doug's friend Skeeter is shown to mostly come off as a ditz pretty often, but in the episode "Doug's Brainy Buddy", he gets a perfect score of 1,000 in the intelligence test, not even knowing it was a test to begin with. If that isn't enough, he is revealed to be quite well read, much to Doug's surprise. His intelligence, as a result, prompts him to transfer to college, which he later turns down due to not being able to air guitar and the college students smoking there as well.
In Detentionaire, Steve pretends to be bad at math so that Greta, who he has a crush on, will tutor him.
Cosmo from The Fairly OddParents! is hinted at to be this. Multiple times, in fact. Cosmo was actually the more intelligent one at the very beginning of the series' run. He sometimes has random bouts of intelligence seemingly from nowhere, only to immediately follow it with another stupid moment.
An episode of Family Guy depicts Lauren Conrad as a closeted genius who, among other things, created a real-life Genesis project. She wants to keep her intelligence a secret because "America doesn't like smart people," which is why George W. Bush got elected twice.
Stewie. In "Leggo My Meg-O" he erases Meg's memory after shooting her suitor and in "Stewie, Chris & Brian's Excellent Adventure" he convinces Chris that he was dreaming.
When Cleveland tries to be an unlicensed psychiatrist, he posits that Adam West is faking his lovable insanity in order to hide his actual, homocidal insanity. West's response indicates Cleveland was correct.
In Futurama it's hinted that Amy might be doing this. She is an engineering student (though in one DVD commentary, the writers admitted that they'd completely forgotten that), so maybe she's a Genius Ditz. It was confirmed in "That Darn Katz". Amy came up with an idea to use the Earth's rotation to generate energy for her thesis so she could finally get her doctorate. She had spent the night before drinking and having sex with Kif and went into the exam in her underwear.
Nibbler, who hides his hyper-intelligence with a mask of ultra-stupidity and a tendency towards doing cute things. He was rather pissed when he later found out that he forgot to erase their memories after his recent escapades, but no one pointed this out to him because they found his antics adorable. He'd been intentionally doing stupid things and was very embarrassed after the revelation.
An episode of Garfield and Friends has Garfield pretending to be an idiot in order to get back some money another cat stole from Odie, and Garfield uses play money to bribe the other cat into giving the money back.
The Darker and EdgierG.I. Joe: Resolute premiere has Cobra Commander stating he was pulling this trope in earlier series, but it didn't work so he's dropping the disguise and getting serious.
It's notable that Cobra Commander kills a lot more people and is much less tolerant of his subordinates attempting to pull crap on him, but otherwise acts just as bonkers as his previous 1980s incarnation, which at least suggests the possibility that he's just saying that to save face.
He's certainly Genre Savvy enough to have backups for both the super weapon and communication jammer, and a bomb shelter that can resist a blast from said super weapon. He is still surrounded by incompetents who went to the Storm Trooper Academy for Accuracy or mouthy psychotics like Zartan and Storm Shadow. They only failed because GI Joe were slightly more competent and accurate. It's quite a different kind of bonkers though; in the old cartoons he'd have some idiotic plot to rule the world by rigging a mayoral election or tricking some rich old man into marrying The Baroness using mind control perfume. In Resolute? He destroys Moscow without warning and hacks his own troops apart.
Although this is crossing into comic book territory, it should be noted that Cobra Commander's original comic-book persona...predating even the original cartoon...was ruthless and crazy since the beginning. From secretly brainwashing his own high command in case they turned on him, to managing a Cobra that actually manages to kill more than a couple of established GI Joes, to even killing his own son Billy in later comics...it's easy to see why the Sunbow cartoon had to tone him down into the bumbling fool we all knew and loved as kids. You don't mess around with Cobra Commander in the comics! As Resolute attempted to go back to his original persona more, the speech about pretending to be a bumbler could be considered something of a nod to this extreme difference.
Grunkle Stan of Gravity Falls is an interesting example, in that viewers are more than aware that he's faking his lack of awareness due to the ending of the first episode showing him retreating into a secret bunker, implying that he has some dangerous secrets of his own. However, the characters themselves don't know this, and he's presented as being totally clueless to the various supernatural occurrences happening around him throughout season 1, even though he personally experienced some of them. Then the season 1 finale comes around, and viewers additionally discover that he's had Journal #1 the entire time and has been working on a mysterious portal in the basement of the Mystery Shack. It's only during the season 2 premiere, where he admits it was a deliberate act, explaining that he hoped his obfuscating stupidity would deter the kids from investigating the town's strangeness themselves. Even then, the other characters remain in the dark about his secret project and how much he actually knows until "Not What He Seems".
Subverted with Old Man McGucket. In "The Society of the Blind Eye", Dipper concludes that the crazy guy is the Author, and his insanity is a cover. It turns his insanity is not only genuine, but an unintentional and self-inflicted side-effect of trying to forget what he learned while working with the actual Author.
In The Grim Adventures of Billy & Mandy, a new kid named Bobby takes over Billy's position as the stupid kid because everyone was sick of Billy, as it turns out Bobby is only pretending to be stupid in order to replace him at his house hold.
In Justice League Unlimited, the Question's conspiracy nut persona is probably an act. At the very least, he isn't entirely imagining things, or having delusions of grandeur about his ability to gather info - this is highlighted by the fact that Batman asks him to ferret out a link between Cadmus and Luthor. When he attempts to assassinate Luthor to stop Superman from doing so, he notes that the Justice League's reputation will survive this otherwise unconscionable action because he is, in his words, "a well-known crackpot".
He then proceeds to spout conspiracy theories in response to every question he's asked under torture, in a more amusing equivalent to a soldier's 'Name, Rank, and Serial Number.'
The Flash did it first, though it wasn't really expanded upon until the Unlimited episode Flash and Substance, where he demonstrated that his happy-go-lucky persona hid a hero who was, perhaps, even more in control of his home city than Batman, all the more impressive because he achieves it all with a smile.
Kaeloo: Episode 138 suggests that while Stumpy is actually quite stupid, he may not be as stupid as he normally behaves.
According to Epileptic Trees about Kim Possible, Ron Stoppable is just acting as bumbling as he is, because if he didn't, Kim would be devastated that Ron is better at life than she is. Cue Evil Ron, who gets to be completely badass.
In an early episode of Kim Possible, Kim rescues Nakasume, a Japanese toy manufacturer, from Drakken and Shego. Nakasume conveys his thanks to Kim by whispering into his secretary Yoshiko's ear, who then translates. Nakasume appears later in the Kim Possible movie So the Drama, in which it is learned that he is actually fluent in English, but enjoys whispering in Yoshiko's ear.
In the season 4 episode "Larry's Birthday", Professor Dementor's henchmen kidnap Kim's RPG-obsessed cousin Larry (wrongly thinking that he was Ron) as part of Dementor's plan to steal Kim's battle-suit. Larry acted like this was just an elaborate RPG scenario and went along with the kidnapping, seemingly siding with Dementor when he managed to kidnap Kim and Ron. At which point Ron (who has played against Larry before) smiles and asks, "Yo, Lar! We looking at a Scenario Nineteen here?" Larry answers, "Precisely," and reveals that he was wise to Dementor's plan and had been wearing Kim's battlesuit all along to keep Dementor from stealing it, and even uses the suit to take Dementor down.
In The Legend of Korra, Varrick initially seems to be a goofy, loud, excitable Uncle Pennybags. He then proceeds to escape Unalaq's blockade with incredible ease and an audacious escape plan, and soon thereafter starts manipulating New Team Avatar into serving his War for Fun and Profit schemes while still feigning friendship.
Looney Tunes: Slowpoke Rodriguez is barely mobile and doesn't think about much aside from his next meal. However, he quickly proves to every bit as dangerous as Speedy Gonzales, thanks to being a crack shot and an expert at hypnotism.
Motorcity: The Duke of Detroit's soldiers do this in the finale, where they cower and generally argue with each other to be much of a help when the heroes (the Burners) are being attacked by Kane's forces, one even notes that his laser has been jammed up with gum. It's later revealed that this was all part of a complicated ruse to get the heroes to think the Duke was weak, and when he actually teams up with the Burners, the guards go on the offensive and successfully fight back the Kane robots and troops.
An episode of Pepper Ann culminates in several characters revealing secrets about themselves including Cissy Rooney, who admits that she plays up the Dumb Blonde stereotype because she doesn't want people to be intimidated by her intelligence.
As stupid as Dum-Dum is on The Perils of Penelope Pitstop, he came up big on Penelope's behalf twice. He used a feather to rescue her from a man-eating plant (throwing it into the plant so it caused it to gag and spit Penelope out) and the nabbing the Hooded Claw's hat and cape so Penelope could win a scavenger hunt. Penelope kissed Dum-Dum each time for his efforts.
The Penguins of Madagascar had a walrus named Rhonda, who started to live in Marlene the otter's habitat as her "roommate". Rhonda proves to be quite an annoyance to Marlene eventually, and she demands the penguins to get rid of her. However, when the penguins did get rid of Rhonda, it turns out that they were right about her being a spy for Dr. Blowhole.
Private's uncle Nigel used this as a cover to hide the fact he was really a super spy. At least until he was caught by The Red Squirrel, who refused to believe it.
Perry the Platypus on Phineas and Ferb does this. He pretends to be a domesticated animal, but every day he goes to work as a secret agent thwarting the schemes of a Mad Scientist.
Bubbles of The Powerpuff Girls is essentially the show's ditzy blonde. "Him Diddle Riddle" twists this on its ear as Him makes the girls take their SATs as part of a series of tasks to save the Professor. Buttercup scores a 35, Blossom a 10, and Bubbles—whose test was patterned out as a flower—scored 1075. Series head writer Amy Rogers points this out as proof that Bubbles is the smartest Powerpuff.
It wasn't known in earlier seasons, but eventually became clear that Maggie from The Simpsons can walk perfectly, shoot people, eat with a spoon, and use the Internet. She just lets everyone believe that she's a normal baby.
This applies to all the bullies. Kerney, despite being a teenager and the father of a teenager, apparently is competent enough to pull his weight at church meetings, for instance.
In the episode "Summer of 4 Ft. 2'', Lisa tires of her usual bookworm self and while on summer vacation plays the part of an average anti-intellectual "cool" kid to win friends. She occasionally slips up, however.
Lisa: Ah, a gift from my favourite crustacean! (Gulps) Rick: Hey, did you learn that word from a teacher for something? Lisa: No...I...heard it on Baywatch. Other kids: Oh yeah!...Baywatch!...David Hasselhoff, man.
A very unusual moment of Obfuscating Stupidity comes from the episode "Mother Simpson"; unusual because it comes from the usually dense-as-brick Chief Wiggum. It's revealed by the end of the episode that Wiggum intentionally led the FBI astray in order to help Homer's fugitive mother Mona escape Springfield, leading one to wonder whether the stupid things he did in the episode were genuine or to just throw the feds off track.
In a deleted scene, Homer tells his mother he's trying to bring the nuclear plant down from the inside.
This spills into many other tropes, from the aforementioned Book Dumb, to Genius Ditz, to possibly even one named after Ralph and many others.
Ralph almost singlehandedly took over the town by acting lovably stupid. (we donít actually know the outcome, since the ending was a cliffhanger after the big reveal).
Some fans believe that Patrick is not actually stupid, but a sociopath that does idiotic and often assholish things on purpose because he knows that his seemingly low intelligence will keep him from punishment. Throwaway comments in some episodes support this view, such as "Home Sweet Pineapple" ("Is it time already to ruin Squidward's day?! SpongeBob, don't start without me!"), "I Had an Accident" (Sandy asks him, "Don't you have to be stupid somewhere else?", and Patrick responds, "Not till four."), and "The Card" ("SpongeBob, you can't always expect my usual brand of stupidity. I like to mix it up. Keep you on your toes.").
Sarah Palin, in South Park's take on the 2008 US election, proves to be far more intelligent when outside the public eye.
Ike of all people if you skipped a few seasons. It is most obvious in "About Last Night...", but by "Fatbeard" it has either become canon or Only Sane Man territory with nobody noticing.
Nathan, a boy with Down's Syndrome who acts as an antagonist to Jimmy. Despite his disability, he actually has no evident mental impairment, but whenever he either needs an adult on his side or needs to hide his actions from them, he'll pretend to be stupid. This is especially apparent in the episode "Crippled Summer", where a Running Gag is that Mimsy keeps yelling out what Nathan's plans are whenever a camp counselor is about to walk by.
Mimsy: Gee wiz, boss, we're gonna kill all the blue team, and Jimmy, huh!?
Counselor Steve: You boys excited for the canoe race?
Nathan: Yes, Counselor Steve. I like the fun canoe.
Baloo from TaleSpin (and to some extent, the original The Jungle Book as well) often seemed very dense and unsophisticated, suffering from endless financial problems and even having trouble spelling correctly. However it was shown many, many times that Baloo is probably a certifiable genius, and it's not just his flying skill (which would put him in line with the Genius Ditz) although that alone is certainly something to boast. Baloo shows an uncanny knack for geography even when navigator Kit isn't around, seeing through deception, insight, philosophy, and even mechanical skill and an abstract understanding of machines (though not to Wildcat's extent obviously). All the more impressive when one realizes that he does all of this based off of instinct, as his denseness is mostly attributed to being largely uneducated (which was somewhat more common in the 1930s when the series takes place anyway), as well as his own lazy nature.
Total Drama World Tour: Sierra is smarter than she lets on. As part of her being a extremely devoted Loony Fan, she knows the show's rules back and forward, and is extremely Genre Savvy; the most stand-out form of this is that she pretends to become Heather's latest pawn while secretly planning to turn it on her.
Word of God is that it's deliberately left open to interpretation whether Uncle Grandpa is actually stupid or if he's The Chessmaster whose screwups are all part of his plan. Lampshaded as early as the third episode, where Uncle Grandpa very obviously and hamfistedly dodges a question over whether he was aware of something that ended up pivotal to the outcome of the episode, or if it was just a coincidence.
Sargeant Hatred of The Venture Bros. pretends to be a bumbling and friendly villain through season three because he knows being nice to Doctor Venture is the best way to get at the Monarch without violating guild rules.
On the good guy side of this trope is Timoty Treister, head of the O.S.I. Who comes off like an insane Teddy Roosevelt, with the personality of Foghorn Leghorn. But as the man himself says he's no "Short-busser" and knows things even the jaded Hunter Gathers doesn't.
Every so often, Wander of Wander over Yonder lets his mask of being an oblivious, daydreaming Manchild slip off and reveal that he knows exactly what's going on around him and how dangerous Lord Hater is.
On The Weekenders, when the gang were looking for dates for the school dance, Lor's suggestion for attracting boys was to pretend to be stupid.
Young Justice: Every member of the Flash family (with the possible exception of Jay). Yes, they're a bunch of happy-go-lucky jokesters, but they are also extremely intelligent when it comes to science. Which is to be expected, given that they got their powers from a science experiment. This is taken Up to Eleven with Impulse, who acts like a little kid in a candy store for his entire introductory episode, after which The Stinger reveals that it's all an act he uses to hide the fact that he comes from a Bad Future.