His hair is the same style as Timmy Turner, except that it's colored green instead of brown.
Cosmo was originally designed as a fat bald lazy slob, a cross between Homer Simpson from The Simpsons and Fred Flintstone from The Flintstones. He was given a black tie to look like he was "always going to work" and to add to the show's 1950's feel.
He and Sparky are the only main characters to never wear Timmy's hat (Timmy wear the hat almost every episode, Poof in "Sooper Poof" (since he was adopted by Timmy's parents) and "Beach Blanket Bozos", and Wanda in "Tons of Timmys").
In the earliest shorts, Cosmo had a deep, suave voice, like a used-car salesman (described by Daran Norris, who also, in the documentary I Know That Voice likened the original voice to a bad imitation of comedian Phil Hartman), and was less moronic, and he and Wanda were both relatively careless and bubbleheaded ("We're two halves of a whole idiot!"). This as since changed, as over the course of the show Cosmo's changed from one half of a fairly goofy couple to the main source of carelessness and trouble, while Wanda's changed into a more sensible character.
Prior to the birth of Poof, he was the last fairy to be born, due to the destruction that he had caused as an infant.
Cosmo and Wanda are the only known Fairy Godparents to have two Godchildren at the same time, though it's implied that since there's a shortage of god fairies that there are others as well.
Before he married Wanda, Cosmo was going to ask the Tooth Fairy for a hand in marriage.
He once bet Juandissimo Magnifico to Wanda for a nickel, which he apparently likes because of its luster. In another episode, he finds a nickel and names it Phillip. Phillip is a girl nickel (as noted in the quotes section below), and is seen in at least one other episode.
Cosmo, along with Wanda has been in all but one episode of the entire series.
There's been several instances he has no brain, but somewhere he has a really tiny one, as shown in the first power hour. But his head is also full of grape jelly, dancer was dancing on his brain one time, and sometimes, elevator music can be heard playing from his head.
He's got a pet hog named Steve that lives in his pants.
In the original cartoon, featured in 'Oh Yeah! Cartoons', Cosmo was actually smart.
Several instances (his name, in Timmy the Barbarian) refer to the name Julius.
His name in Greek means "world".
He supposedly wears a diaper. He has been seen wearing underwear most of the time, but after Fairly Odd Baby, he was seen wearing diapers throughout the show.
All of Cosmo's pets are named from Jimmy Neutron Characters (Carl the Ant, Cindy the Bee, Jimmy the Cat).
He often flirts with other female characters he deems attractive (e.g. Tooth Fairy) which often angers Wanda. He has also fallen for Princess Mandie, Blonda Fairywinkle, his reflection, a doll that was later transformed into Tootie, & various others.
He is the only fairy to go through an on-screen Fairy Pregnancy.
He likes rice, pie, corn, lemonade, pudding and churros.
His favorite flower is the rose as revealed in the video game, "Shadow Showdown".
Cosmo's old band is called The Fairies. It consists of himself on the electric triangle, Eric Clapton on the guitar, Pan on the pan flute, Santa Claus on drums, and Ludwig van Beethoven on the organs.(They were seen in Boys in the Band)
Cosmo and Wanda as The Fairly OddParental Controls
Cosmo, along with Wanda, appears in "The Fairly OddParental Controls", a parody of "The Fairly OddParents" in "MAD".
Cosmo is allergic to nuts, revealed in the "Squirrely Puffs" episode, although in past episodes he has been seen eating nuts without allergic reactions. The nuts he ate in Squirrely Puffs may have been a special kind of nuts that he is allergic to or that Cosmo takes a medication to prevent having an allergic reaction to nuts.
In the anime series, Sonic X, there is a character known as Cosmo in its third season. While both characters have the same name and color of hair, the only 2 differences is that they have opposite genders and different eye colors.
He is apparently the reason why Denzel Crocker lost both him and Wanda due to allowing himself to be revealed to humans.
Darran Norris who voices Cosmo also voices over many male characters of the show including Anti-Cosmo and Jorgen von Strangle.
Cosmo's brain is probably located in butt according to Balance of Flour but other episodes strongly disagree with this.
According to the episode, "The Gland Plan", Wanda stated that Cosmo was an only child but in the episode, "Double-Oh Schnozmo" his brother Schnozmo visits.
He was shown in the Big Time Rush episode, Big Time Cartoon, and Budda Bob acted, talked, and being like Cosmo when he hit his head falling out of the ladder.
It is also revealed in Turning Into Turner that Cosmo doesn't weigh any pounds.
Cosmo is highly allergic to potato chips and nuts.
In Tons of Timmys, it is revealed that Cosmo does not have a birthmark on his butt.
In A Sash and a Rash, it is revealed that Cosmo is allergic to peaches.
In This is Your Wish, it is shown that Cosmo lived with his mother before he married Wanda but in The Fairy Beginning he stated he lived with his Uncle Harry and Aunt Potter
