Sheldon 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):

Sheldon's basic appearance
Full Name Sheldon
Gender Male
Species Horseshoe Crab
Family and Relations
Ammoses Shellendorf (grandfather)
First Appearance Splatoon (2015)
We’ve just confirmed that this horseshoe crab dude is the owner of the weapons shop. He’s reportedly obsessed with all types of military gear. This love has come at a cost, though, as cleaning and polishing his gear all day every day has apparently made him extremely nearsighted. No wonder his glasses are so thick. What a nerd!
Splatoon Official tumblr

Sheldon is a Horseshoe Crab character from Splatoon. He acts as one of the shopkeepers in the game, owning the store Ammo Knights and selling weapons to the Inklings. According to early press information, he is obsessed with military gear, and teaches the Inklings how to use the weapons. He is extremely nearsighted, having become this way due to the long hours he has spent polishing and cleaning his gear.


Names in Other Languages

Language Name Meaning
GermanArtyName resembling Artillerie (artillery).
ItalianArmandName resembling armatura (armor).

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