Not a serious character. Oh, they're officially in canon, but no matter what exploits they accomplish, you won't see it referenced much. That's not what fans are looking for. These are "Funnybook" characters who are actually funny. Any use of them is usually restricted to their own book, where they can do wild and fun stuff. They are solely for positive consumption.
Sometimes the character isn't even used that often, but their presence fuels conversation within fandom. Often such characters become a meterstick for fans: One camp claims they're too silly or insulting to continuity, while the other says comics can be fun and these fans should lighten up.
Actual writers seem to pick up on this, and don't usually dare more than cameos in "serious" books.
Beware trying to make these characters Darker and Edgier; you'll get flak from both the people who liked them, and the people who dislike them, and don't care how many guns or pouches you strap to them.
Opposite trope to Knight of Cerebus; the Sanguine member of a Four-Temperament Ensemble.
Spider-Man is one of Marvel's Light Hearted and prominent cheerful Nice Guys, and the most upbeat of the Avengers. Despite his angsty and troubled life, Peter Parker most of the time takes serious and depressing situations and turns them into amusing cracks at people and humorous antics in any given time.
And his Love Interest Mary Jane Watson, before it was later revealed that this was all to cover up her insecurities and troubled life at home.
And don't forget Peter Porker, the Amazing Spider-Ham.
Although She-Hulk is more prominent, Marvel's flagship character for this trope is Doreen Green, better known as Squirrel Girl, whose silly powers and low actual presence in comics nonetheless have helped her beat a number of supervillains. She actually defeated Dr. Doom once, which lead one writer to retcon that as being Actually a Doombot which led another writer to have her defeat Thanos offscreen and then have Uatu the Watcher show up to officially proclaim it as "not a robot, clone, or simulacrum."
Just to show how the feud continues, subsequent comics have had Thanos reveal that he has perfected a means of creating weaker copies of himself that could fool The Watchers.
Note that both She-Hulk's current comic and all of Squirrel Girl's recent appearances are written by Dan Slott, who pretty much epitomizes the "comics should be fun!" attitude. Slott wrote both the above mentioned items, thus feuding with himself!
Squirrel Girl is infatuated with Robert Baldwin, the superhero known as Speedball, who was also one of these for most of his career — prior to turning Darker and Edgier as Penance. He's Speedball again now, but he's still not quite his old fun-loving self.
Irving Forbush (also known as his "superhero" persona, Forbush-Man) is an earlier Marvel character (circa 1967) who fits this trope. He was the main character of Not Brand Echh, a '60s superhero parody comic, and What The—!?, an '80s/'90s superhero parody comic.
Which makes the evil psychic clone of him in Nextwave all the funnier.
The DCU's Ambush Bug qualifies as well. He first appeared as a fairly standard supervillain, but within just a couple appearances had jumped into outright comedy, making fun of the fan obsessions of the day.
Marvel's Deadpool started out as Rob Liefeld' stand-in for DC's Deathstroke the Terminator. Nearly every other writer since has used him as a comedy character, to the point of having him become entirely aware of his nature as a comic book character. His Ultimate Marvel counterpart is (almost) entirely serious, but there are hints that might not have actually been him.
It's rumored that Dan DiDio, DC's current Editor-in-Chief, dislikes "silly" comics, which is why many ex-JLI members have died under his reign (well, the lucky ones died, anyway); it's more likely due to the fact that most of them haven't been in the public eye for years, leading to becoming C-List Fodder.
Meanwhile, Gold and Rip Hunter are actively exploiting Booster's reputation as a second-rate hero to let him fight time-traveling opponents who would smother Booster in his cradle if only they figured out he was the problem.
Keith Giffen also fathered Lobo with Roger Slifer, which is a Badass Biker coupled with professional wrestling camp and biker humor. The plot is always silly, including Lobo working as a mascot in a crappy amusement park, or the time the writer is wired to a jokes detector shocking him for each "adult joke", turning Lobo into Superbo, a Silver Age Superman ripoff to make him family friendly, or other nonsensical stuff as the crossover Lobo vs The Mask, or the mini-series Lobo's Back, about his failed resurrections.
In one issue of Avengers: The Initiative, he was shown brutally attacking Camp Hammond instructor, Gauntlet, for using the New Warriors name as an insult, nearly killing him in the process. This has been seen by some as an Out-of-Character Moment, though others see it as not really being far off from his normal cartoon-ish prankster nature and shows his loyalty to his teammates, who he he even tried admitting the act to, before getting interrupted. For now it seems that Iron Man villain Ghost has been blamed for the act.
Iceman, in an early issue of X-Men: First Class, calls himself "The Bringer of Fun", and throughout the series generally acts like a lovable dork.
In New X-Men this role is taken by both Santo (Rockslide) and Megan (Pixie). Megan who is just too cute and causes hallucinations of teddy bears and unicorns... to Wolverine. And Santo is the kind of jerk you gotta laugh at, roasting marshmallows over his classmate's head, or scaring his classmate worried about being killed by EXPLODING next to him on the sofa randomly.
The DCU also has Bart Allen, aka Impulse, later Kid Flash, who even in his more serious Kid Flash incarnation was still epically hilarious. Then, came his run as The Flash. He died, for those who didn't know.
Stephanie Brown aka Spoiler, Tim Drake's girlfriend in Batman. She was temporarily killed off, but she was brought back through an Author's Saving Throw and had a fun run as Batgirl before the reboot.
A subversion of this kind of character comes in the form of Kid Devil. Joining DC's Teen Titans after Kid Flash left, he was made to seem like the comic relief member of the team. However, unlike most of these characters, he was neurotic, envious, and very self-conscious. He projected a fun, optimistic attitude to hide his insecurities and the fact that he had sold his soul to get his powers. These shortcomings did a lot to make him more than just Kid Flash's replacement. His teammate Miss Martian comes closer to the spirit of the trope.
Miss Martian was from the evil white martian race, but rejected that entirely to be one of the most bubbly characters in comics. At one point she got an evil side in her head, who she fought off via happy thoughts of puppies.
Marvel has yet another fun personified character in the from of Morph from the Exiles.
Nightcrawler of the X-Men was originally goofier, liked having fun, and played pranks all the time. Some of later versions of him downplay this quality or remove it entirely, depending on who is writing it.
The original Marvel Excalibur was an example of this trope until being reimagined as just another Dark Ages X-book. The original idea was the most "fun" members of the X-men (Nightcrawler and Kitty Pryde) form their own team of European superheroes when it appears the other X-Men are killed. They were joined by other Fun Personified characters in the process.
Warlock of the New Mutants was (and since his recent resurrection, probably will be again) basically a walking scribble made of semi-organic circuitry, prone to bizarre behavior and random shapeshifting (the "can turn into anything" brand of shapeshifters are heavily represented in this trope).
Season 1 of Who Wants to Be a Superhero? had Major Victory, a flamboyant, over-the-top Flying Brick type of character, who was eventually eliminated for not taking heroics seriously enough... oh, and for having once been a male stripper.
...despite rescuing a crying girl, being helpful and nice to anyone and everyone, and walking across a backyard with a full-grown attack dog hanging from each arm without breaking character.
Subverted in a sketch on Important Things With Demetri Martin. "Bruce the Funny Dog" gives a glimpse of what it might be like to actually live with Fun Personified. Every time the camera cuts to Bruce the basset hound, he's wearing a different wacky outfit. This doesn't go over so well while his owners are dealing with a family tragedy.
Subverted by the Seventh Doctor, who was originally Enforced into this character type as a Lighter and Softer reaction against just how much Bloodier and Gorier the show had got during the Sixth Doctor's run. he spent the first season playing the spoons, doing magic tricks, being a figure of delight and whimsy and battling Camptacular comedy enemies with the loosest continuity yet. Then a new writer took over, who introduced 'comedy' monsters but played their effects in a dark and serious way (like the Kandyman and the Killer Clowns) and revealed the Doctor's apparent silliness was Obfuscating Stupidity, and Seven became one of the most alien, manipulative, and dark Doctors of the lot. When the series got cancelled the Expanded Universe picked him up and used him to codify all of the "Dark Doctor" tropes that the revival series later handled on-screen - like a serious examination of the Omniscient Morality License, Angst? What Angst? and the psychological profile of someone who'd do that much Dirty Business. In the New Adventures books, there's even a line that he doesn't play the spoons any more because he's too busy toppling empires.
The Expanded Universe gives us the loopy lady time-traveller Iris Wildthyme, an in-universe parody of the Doctor with a time machine that's smaller on the inside, a happily sexual personality to contrast with the Doctor's Chaste Hero status, a tendency to take on handsome young male companions, and a deadly rivalry with legendarily pathetic-looking monsters the Zarbi. She occasionally crosses over with the Doctor in some sillier short stories.
Big Finish Doctor Who often uses Mel like this - the Sixth Doctor's relationship with Peri (and Evelyn) and the Seventh Doctor's relationship with Ace are both extremely complicated. Mel is played by an over-the-top actress who did mostly musicals and Panto, and has a sillier relationship with both her Doctors and Timey-Wimey Ball writing that means her entire character makes no sense at all, so audios featuring her are usually Breather Episodes between grittier storylines featuring Peri or Ace.
Hiro Nakamura of Heroes was originally written because the creator's wife pointed out that none of the heroes created so far actually enjoyed their powers. Since Heroes has Loads and Loads of Characters, that means loads and loads of "Having powers is AWESOME!" meant to be spread over a dozen or so people ended up condensed into one happy little Japanese man.
Daft Punk. They take the enjoyment of their fans VERY seriously. Their iconic robot look is a way for fans to immerse themselves into the music and its themes.
*NSYNC were noted for frequently poking fun at themselves and their music videos and concerts were seen as more fun, especially since their chart rivals Backstreet Boys were more often portrayed as quite stoic and Perpetual Frowners.
Buckethead is usually this to his fans. He's always masked and in character, wearing a fried chicken bucket on his head and acting in a childish, slightly creepy manner. He also decorates his rooms and stages in a spooky-silly sort of way, frequently does robotic dances and nunchaku demonstrations when performing, and trades toys with the audience.
Paranoia has been a darkly humorous game since its inception, though the degree of zaniness tends to vary with the specific GM involved. In the latest version of the game, however, this is codified with the "Zap" game style, which specifically caters to Fun Personified players.
Star Fox: Panther Caroso is somewhat showing characteristics of this, at least when compared to Wolf or Leon. In fact, he's usually the subject used in various Japanese meme vids.
BlazBlue's Taokaka is despite her fearsome face, utterly adorable and possibly the only character without a hint of angst and tragedy. Her voice helps too. Not to mention the extra-strength Les Yay with "Boobie Lady". Bang comes close, but he's got his own baggage.
Makoto Nanaya seems to fill this role as well to a lesser extent, being a Genki Girl with a similarly cute voice and a propensity to utter completely silly things during a fight such as The Tick's catchphrase "SPOOOON!!" It helps that she happens to be an expy of Squirrel Girl.
Freedom Force vs The Third Reich has the Green Genie, who manages the impressive feat of being Fun Personified by comedy Silver AgePastiche standards. She zooms around on a magic carpet, turning Nazis into flowerpots.
In Saints Row 2, one of the new Saints, token girl Shaundi, fulfills this role. Really Gets Around combined with Cloud Cuckoo Lander combined with a New Age Hippy style set of interests makes her one of the most entertaining characters in the game. Sadly, this characterization isn't kept in the next game.
And to a lesser degree, Johnny Gat takes the form of a Dark Humor styled one. Almost everything he does is either act like a lovable psychopath or do something inhumanly badass.
For every badass monster in Pokémon, there is at least one other monster that's meant to be just cute or silly or have a "gimmick" to them. They usually end up as Joke Characters or maybe as Lethal Joke Characters if they are lucky. Baby Pokémon are a great example.
In Dragon Age II, Hawke with the Sarcastic Personality is a nigh-unstoppable screwball in charge of protecting Kirkwall, cheerfully snarking at everyone and everything in the game. Of course, we later see that this is mostly an act designed to cover up the fact they're really just a Sad Clown, particularly after their mother's murder.
Chaka of the Whateley Universe really fits this too. She's anti-Wangst, and constantly getting into silly adventures (being attacked by Tigger while trying to go on a date?). In the serious adventures, she's one of the ones constantly throwing out one-liners.
Even more so than Chaka, Beltane (Kendall Forbes) and Thorn (Bob Rose, not the other Thorn) are in it for the wacky antics. Both have the power of creating and controlling ectoplasm, and both use it mainly for practical jokes. They seem to have a big joke-war going on off-camera now, and innocent bystanders keep getting turned into Pokemon or Easter eggs or things like that.
Chuckles the Happy Clown, who not only lives up to his name, but was one of the most effective crimefighters in the history of the Global Guardians PBEM Universe. Donato Spinelli, the player of the character, was generally thought as being the greatest roleplayer anyone had ever met, or had the pleasure of interacting with. He was able to make a truly funny joke while in the middle of the dourest of situations without once ever becoming a Snark Knight.
Regular True Capitalist Radio caller 213 AKA Ghetto Capitalist. He often calls in the middle of a party and brags about how they're eating ribs and drinking beer. Knowing how he funded the party, this angers TCR's host Ghost.
Breeze Rider from Dusk's Dawn cracks (bad) jokes many times in the short and tends to be a daredevil… if flying through a forest counts.
The Cyantian Chronicles: Quinn, who (almost) never ceases smiling and trying to cheer everyone else up. Darius shows some of the requisite traits, though he's more prone to the not-happy side of emotions.
Dr. Randy Disaster of Gunnerkrigg Court counts both because he teaches the most popular class in the school, and because of his fantastic entrance: He busts into a classroom (and into the story!) with no prior warning whatsoever, and drags everyone off into a ridiculous Space Opera simulator.
Grace in El Goonish Shive. Bubbly to the extreme, she is insanely happy for someone who was made in a lab and witnessed the entire research staff being murdered by someone who physically and emotionally abused her for several years before she ran away. She is capable of being serious (especially whenever any of those things are brought up), but for the most part she exists to be cute and funny, which is what makes her so endearing.
Lord Ikarion Daryil in Project Future , a DMFA fancomic. In the current arc (strip 170 and 171 ) he celebrates his ascension to tri-winghood by cosplaying as Jesus based on Ruling Class.
Molly the Peanut Butter Monster from The Inexplicable Adventures of Bob! A fuzzy pink girl-thing with a peppermint-striped tail, and pom-poms growing out of her head. Cheerful and childlike, she enjoys building impossible machines and writing crack fanfics. She revels in the fact that she can run around naked because she's furry.
While Super Mega Comics has never been serious, it does poke fun at this trope with "Everybody Man".
Jade played this role too, being fun and bouncy, having game-based fetch modi, and being designed as a parody of the Mary Sue concept. Would engage in wacky antics like fake-fighting her grandfather and dog respectively, mess around with time and space like it was nothing special, and be generally Adorkable. Then she accidentally brought back her dead and severely traumatised dreamself, started talking to Karkat, and got stalked by Jack Noir. The fun, shall we say, toned down quite a bit.
Spam from Zoophobia is this. He's silly, wacky, and lively, and is never serious.
The Flash mostly takes this role for the DCAU, even in his (very, very slightly) serious moments.
Nightcrawler in X-Men: Evolution is this, matching up with how the original Nightcrawler was in the comics.
Likewise, Toad is this for The Brotherhood. It's to the point that a large majority of the shows comedy is derived solely from him.
Beast Boy on Teen Titans. His comic self, while funny, could also be somewhat of a jerk too often to qualify as pure fun like Kid Flash, but his animated self definitely qualifies.
Naturally, Kid Flash in his Season 5 appearance follows this trope too.
Subverted with Terra in the show, whose Fun Personified demeanor is to hide that she has BIG ISSUES.
Pepper Potts from Iron Man: Armored Adventures thinks that being a superhero is this and thus really wants to be one because of how fun it is; even when Rhodey tells her that Tony was almost killed last week, Pepper responds with 'See?!'
The animated version of Beetlejuice, probably moreso than his original film version.
From Avatar: The Last Airbender , Aang started out as this - an interesting case, since he's the protagonist. He was bubbly fun personified - of course, as the series progressed, and the guilt mounted, this began to diminish.
My Little Pony: Friendship Is Magic has Pinkie Pie, who is the literal personification (ponyfication?) of the Element of Laughter, which is about as literal as the title of this trope gets. Her solution to every problem is to throw a party, and she won't hesitate to throw a party even if there's no reason to do so. Even in the episodes where she has real character development, she will readily defy reason and reality for the sake of a gag. Justified in that her motivation for almost everything is to make her friends smile — and she considers everyone to be a friend.
"Too Many Pinkies" deconstructs this when Pinkie uses a magic pond to create copies of herself to spend time with all of her friends. The copies lack all of Pinkie's traits outside of being Fun Personified and are wholly committed to having fun. Worse, they are so dedicated to having fun that they bother everyone around them. The real Pinkie is driven to tears by her copies' antics.
Spike, too, although he gets more development beyond the traditional sidekick.
James Baxter the Horse from ''Adventure Time has the uncanny ability to cheer up anyone by dancing on top of a beachball while neighing his name. Finn and Jake try to imitate his act and fail horribly, so it seems only he can pull it off properly.
Following Christopher Reeve's paralyzing horseback riding accident, Williams, his former classmate at Julliard, cheered him up by pretending to be an eccentric Russian doctor, saying he was there to perform a colonoscopy. Reeve stated that he laughed for the first time since the accident and knew that life was going to be okay.
Michael Jackson wanted to be this; always trying to find ways to entertain people. He spent a ton of money converting his house into an amusement park.
Let's face it, we all know at least one person like this. Chances are we are it.