Humans are an extinct species that once populated the world 12,000 years ago, before the start of the Mollusc Era. It is stated that the rising sea levels caused the extinction. Many remaining artifacts from the humans are still present and discovered by the current inhabitants, such as Inklings. Human fossils and bones have been found and are exhibited in museums, and most technology has seemingly been developed by reverse-engineering human designs.
Currently, the only specific human being that is known is the "professor", which created Commander Tartar, an AI designed to pass down humanity's knowledge to the next evolved life but reprogrammed itself to recreate life to its specifications after deeming Inkling and Octarian society unworthy of its knowledge. The professor was also Judd's previous owner, where the human cryogenetically sealed Judd in a machine to preserve him for the future. The machine is also capable of creating a clone of Judd, as the human feared that the cat would be lonely.
- In the dialogue for Shellendorf Institute, Pearl mentions that she has dug up human bones before, to which Marina replies that they are found everywhere.
- The Art of Splatoon expands on Splatoon's background story, in which it was revealed that the extinction was caused by a nuclear missile detonating on Antarctica during one of many previous wars, which melted its ice cap and worsened the already rising sea levels.
- In the same art book, it is also implied that humans created the domes found in Octo Valley as a shelter during the flooding.
- The NILS Statue resembles a giant human being; more specifically, the mythological Greek god Hermes.
- Some Inklings and Octolings may believe humans were never real, as Marina stated "I wish humans were real".
An image of a human being with Judd in Octo Valley's scroll 25.
Art portraying a human displayed in Museum d'Alfonsino.