"Agent 3" and "Agent 4" are the protagonist Inklings of Splatoon's and Splatoon 2's single player mode, Hero Mode, and the player's character in multiplayer modes, respectively. They can be male or female, and their hair 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 (who are Agents 1 and 2 respectively).
In Splatoon 2, Agent 3 is away with Cap'n Cuttlefish, so another Inkling, the protagonist "Agent 4", follows Marie to find her missing cousin Callie and stop another Octarian theft of the Great Zapfish.
Agent 3 can have a variety of appearances, depending on the player's choice of gender, skin color, and eye color, as well as their current ink color. They wear the Hero Suit, and can pick up Armor to wear as well. They wield the Hero Shot by default, but can use a Charger or Roller for amiibo challenges.
Agent 4 can have a variety of appearances, depending on the player's choice of gender, skin color, eye color, and hairstyle, as well as their current ink color. They wear the new version of the Hero Suit, and can pick up Armor to wear as well. They wield the Hero Shot by default, but are later able to use a variety of other Hero weapons given to them by Sheldon.
Not much is known about Agent 3's background, except that they are at least 14 years old, since they have complete control over their squid and humanoid forms.
Agent 3 initially went to Inkopolis for an unknown reason, but got swept up in Cap'n Cuttlefish's quest to save the Great Zapfish. In Octo Valley, Agent 3 completes various missions to retrieve stolen Zapfish, defeating many Octarians along the way. Eventually, Agent 3 confronts DJ Octavio, rescuing the Great Zapfish and restoring Inkopolis' power supply.
Agent 4 initially went to Inkopolis for an unknown reason, but got swept up in Marie's quest to save the Great Zapfish and her cousin Callie. In Octo Canyon, Agent 4 completes various missions to retrieve stolen Zapfish, defeating many Octarians along the way. Eventually, Agent 4 confronts DJ Octavio and a brainwashed Callie, rescuing the Great Zapfish, freeing Callie, and finally restoring Inkopolis' power supply.
- Two sets of Gear identical to Agent 3's outfits can be unlocked for online play.
- After completing Octo Valley, the player is rewarded the Hero Headset Replica, Hero Jacket Replica, and Hero Runner Replicas.
- At Levels 25, 30, and 35, Judd will give the player the Armor Helmet Replica, Armor Jacket Replica, and Armor Boot Replicas, respectively.
- Agent 3's canonical gender is female, as depicted in the second Sunken Scroll in Splatoon 2.
- As of Splatoon 2, Agent 3 is on a mission with Cap'n Cuttlefish.
- In the English translation of Splatoon 2, Marie remarks to Agent 4 that Agent 3 has fairly poor hygiene.
- Based on Marie's dialogue stating that Agent 4 is "two years older" than Agent 3, one can assume that Agent 4 is at least 18 years old, as Agent 3 was about 14 years old around the events of Splatoon, and would be around 16 years old during the events of Splatoon 2.
- This has been a topic of confusion and debate within the community, with many believing Agent 4 to still be 14, noting the inklings' similar physical appearance to those of the first game. Marie's statements which would make Agent 4 roughly 18 years old also contradicts a statement made in an interview with Splatoon 2 producer Hisashi Nogami that "The previous playable Inklings would be around 16 now, so the new 14 year old Inklings will step up to the plate. The playable Inklings will still be around 14." It is unknown if this is an oversight or not.
- It has also been suggested that Marie's dialogue is a meta joke, directed not towards Agent 4, but towards the player who controls Agent 4 themselves.
- It can be presumed that Agent 4's canonical gender and appearance is that of a female inkling with short tentacles, as there are no available images of a male Agent 4, and all promotional art has depicted Agent 4 as such. This is in contrast to the first game, which had multiple official art depicting both a female and male inkling as Agent 3.
- This is further evidenced by the final portion of the end credits, which depict a female Agent 4 celebrating alongside a reunited Callie and Marie.
- One of Marie's dialogues when spoken to in Octo Canyon, reveals that she finds Agent 4 to be "pretty adorable".
- She also states that Agent 4 has much better hygiene than Agent 3.
- Agent 4's ink color varies based on the mission, it is also a specific color depending on each sector of Octo Canyon. They have yellow ink on Sector 1, green ink on both Sector 2 and Sector 5, and teal ink on both Sector 3 and 4.