Agent 3 or Captain is the protagonist Inkling from Splatoon's single player mode, Hero Mode, and the player's character in multiplayer modes, respectively. They can be male or female, and their hair, skin tone, and eye color may vary, depending on the player's choice of customization.
As they are the Inkling who joins Cap'n Cuttlefish's New Squidbeak Splatoon to rescue the Zapfish, they are known as "Agent 3", as the other two Agents are the Squid Sisters, Callie and Marie(Agent 1 and 2)