"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.
Drop down the information below with caution unless you have completed Hero Mode or Octo Expansion. Spoilers are below.
Agent 3 returns in Splatoon 2's Octo Expansion. Agent 3 retains their original Hero Suit, now also wearing a gray torn cape with a number "3" in Inklish. When Agent 8 collects 3 of the Thangs, Cap'n Cuttlefish will decide to make a "Missing" poster for Agent 3 which will have the player determine Agent 3's gender, skin color, and eye color.
After Agent 8 collects all four of the Thangs, the Telephone builds it and tricks them and Cap'n Cuttlefish inside to kill them until Agent 3 busts in from the ceiling and destroys the blender, responding to the CQ-80 distress signal. Agent 3 is then rendered unconscious and Cap'n Cuttlefish stays behind to look after them as Agent 8 goes through the hole Agent 3 made. The remains of the Telephone then attacks Agent 3 which has their mind partially sanitized and hijacked into tying up Cap'n Cuttlefish and attacking Agent 8 before they can leave.
After being defeated, Agent 3 is once again unconscious and wakes up after Agent 8 defeats the NILS Statue and Commander Tartar and now has a band-aid on the back of their head on as the staff credits roll. When Agent 8 comes back to the Deepsea Metro, Cap'n Cuttlefish tells them that Agent 3 went back on patrol, explaining their absence. After Agent 8 completes all the tests, a locker in the Central Station will open and Agent 8 will remember everything to their battle with Agent 3 which prompts another arena fight between the two agents.
Agent 3 is armed with their Hero Shot Replica has an arsenal of Special weapons at their disposal. They will always enter the arena by a Super Jump and activate Splashdown upon landing. They'll go after Agent 8 while throwing bombs and their Hero Shot has the fire rate of a regular Splattershot, they're also able to swiftly dodge away similar to the Drop Roller ability when taken hits by Agent 8's Octo Shot.
There are different phases which has Agent 3 use different specials: They'll use the Baller, the Curling Bomb Launcher, the Sting Ray, and repeated Super Jump Splashdowns. Agent 8 can shoot the Baller to stop Agent 3, shoot at Agent 3 when deploying Curling Bombs, throw bombs when using the Sting Ray, or shoot at Agent 3 when they briefly stop after using the Splashdown.
The battle of Agent 8 and Inner Agent 3's has them don the classic Splatoon colors of blue and orange, respectively. Inner Agent 3 now has different specials at their disposal as well as having Autobombs instead of Splat Bombs. Inner Agent 3's Hero Shot has no spread to it and will always shoot straight.The arena is now significantly smaller with no inkable walls or platforms with only the floor being the only inkable surface. With each phase, Inner Agent 3 has a different special: Inkjet, Bubble Blower, Autobomb Launcher, and Tenta Missiles along with Splashdown. When defeated, Agent 3 is called "Inner Agent 3", representing Agent 8's inner hero.
Spoilers end here.
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 most likely female, as depicted in the second Sunken Scroll in Splatoon 2 and the Octo Expansion trailer.
- 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 most 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.
- No matter what bottoms they choose to wear, Agent 4 will wear the standard shorts from the first game when wearing the basic hero suit. They will wear the shorts and tights if they're male or the longer pants if they're female if they pick up armor.
- It's revealed that Agent 4 (and presumably all inklings) wears a sports bra (if female) or a tank top (if male) under their clothes when they're splatted in their basic hero suit.
- It's revealed in the Octo Expansion's art book that DJ Sango (Agent 3's rapper name) and Marina were supposed to have an eight hour long rap battle.
- Agent 8, their Octoling counterpart in Octo Expansion.