Hero

Hero commonly refers to Agent 3, Agent 4, Agent 8, or the second Agent 3, the protagonists of the single-player modes Octo Valley, Octo Canyon, the Octo Expansion, and Return of the Mammalians, respectively. It may also refer to the single-player modes themselves, also known as Hero Mode. Other things it may refer to are:

The suits worn by the New Squidbeak Splatoon:
 * Hero Suit
 * Armor

The replica gear based on those suits:

The main weapons used in Octo Valley, Octo Canyon, and Return of the Mammalians:
 * Hero Shot

The replica main weapons based on these weapons:

The Splatfest:
 * Hero vs. Villain