This is a list of characters that appear in the Splatoon series, such as Splatoon, Splatoon 2, Splatoon 3, and more. This list will have the English names of the characters. For their Japanese names check their individual articles.
For the artists in the Splatoon world see List of Artists in Splatoon.
For the characters from the CoroCoro Comic manga series see List of CoroCoro Splatoon Characters.
Note that Octolings are a subspecies of Octarians. Humans are the only one listed that are presumably extinct.
Animals relates to animals in real life. The so far known animals in this world are birds (sparrows, gulls, ducks, and pigeons), cats (Judd and Li'l Judd), nudibranchs and bugs (butterflies, crickets and cicadas). Dogs and turtles, whether or not if extinct, have been shown in Splatfests.
Nudibranchs have only been shown as art at Museum d'Alfonsino, it also seems like they are pets.