At which E3 presentation was the first Splatoon revealed?

The first Splatoon was revealed at Nintendo's E3 2014 presentation.

Nintendo introduced Splatoon in a trailer during its E3 2014 Digital Event, presenting it as a colorful, competitive Wii U shooter built around firing ink and claiming territory. A playable multiplayer demo was also available on the show floor, allowing visitors to try its four-versus-four Turf War concept.

The reveal was notable because Splatoon was a new Nintendo intellectual property rather than an established Mario, Zelda, or Pokémon spin-off. Its protagonists, the Inklings, could transform between humanoid and squid forms, swim through their own ink, and use ink coverage as both movement and combat strategy.

The game's single-player content was not the main focus of the initial reveal. Nintendo later explained the story campaign, Octo Valley, through a subsequent Nintendo Direct. Splatoon ultimately launched worldwide between May 28 and May 30, 2015, for Wii U.

The main confusion is between the reveal and later promotional events. E3 2014 introduced the game, while E3 2015 occurred after the original title had already been shown and was closer to its launch period.