Jelonzo did not originate from fanon, and more information can be found on their respective wiki(s). You may read more about it on the following wiki(s):

This is Jelonzo, the charismatic clerk that runs the clothing shop. With his uncanny sense for the hottest trends, he’s viewed as a fashion god of sorts by all the young squids in town. He hails from distant waters and has a strange way of speaking that can make it difficult to understand him, but that may be one of the secrets of his success.
Splatoon Official tumblr

Jelonzo's basic appearance
Full Name Jelonzo
Gender Male
Species Jellyfish
First Appearance Splatoon (2015)

Jelonzo is a jellyfish character from Splatoon. He acts as one of the shopkeepers in the game, selling various t-shirts - of the male, female and unisex variety - to the Inklings in his store Jelly Fresh. Despite being a clothing store clerk, Jelonzo refuses to stock pants. This is presumably due to him being unable to wear them.


Names in Other Languages

Language Name Meaning
Possibly derived from ゼラチン zerachin (gelatin).
SpanishM. DusoFrom medusa (jellyfish).
FrenchG. LatineuxFrom gelatineux (gelatinous).
GermanJean-QualleFrom the name Jean, and Qualle (jellyfish).
ItalianMedusoFrom medusa (jellyfish).

Splatoon series
Splatoon 2: Inkvasion | Splatoon 3 | Splatoon X | Splatoon: Artistic Onslaught | Spla2n | Splatoon: Ink Wars | Splatoon: Code Angkor | Splatoon: Event Inkdown | Splatoon: L.A.N.O.X
Species Inkling | Octarian | Jellyfish | Zapfish | Salmonid
Protagonists and Allies Agent 3 | Agent 4 | Judd | Li'l Judd | Cap'n Cuttlefish | Squid Sisters (Callie | Marie) | Annie and Moe | Jelonzo | Crusty Sean | Sheldon | Spyke | Great Zapfish | Off the Hook (Pearl | Marina) | Flow | Jeflonzo | Bisk | Murch | Diana | Nathan
Antagonists and Enemies DJ Octavio | Octoling (Elite Octoling) | Octotrooper (Shielded Octotrooper | Octodiver) | Twintacle Octotrooper | Octoball | Octocopter | Octobomber | Octostriker | Octosniper | Octostamp | Octopod | Squee-G | Flooder