The Deep Sea King (深海王, Shinkaiō) ruled over the Seafolk as their king, and claimed the deep sea as his own. He is the main antagonist of the Sea Monster Arc.
On land, the Deep Sea King is the most humanoid of all the Seafolk, though it is revealed that he only looks like this when he is dehydrated. Sporting an aquamarine color, he is a large, muscular being with dark skin covering his arms, legs and back with his chest and stomach being a lighter color. He has fins on the side of his face, sharp eyes and large fangs. He has a small pink oval over each eye, similar to eyebrows, and another at the corner of his eyes. He wears a red speedo, a large, fur-trimmed cape held together at his chest with a clasp in the shape of a fish head, and an ornate crown. The most striking feature of the Deep Sea King is that he has a heart where each of his nipples should be.
When he is properly hydrated, he shows his true form. He becomes much larger, his muscles expanding dramatically. The fins on the side of his face and back grow much larger and develops new fins on his forearms and shoulders. His face becomes significantly more monstrous, with his eyes and mouth becoming larger, distorting the other features of his face.
The Deep Sea King is a rather sadistic individual, who enjoys causing pain in others and starting fights. He is determined to take the surface world for himself to rule. He regards people as little more than food and has no qualms about treating them as such. He is also very arrogant and prideful, considering himself to be better than everyone and stating that he stands at the very top of the pyramid of all living organisms on the planet.
Hero Association SagaEdit
Sea Monster ArcEditAfter the underlings he had sent to attack J-City were defeated at the hands of Stinger, the Deep Sea King himself decides to come up to the surface himself and wreak some havoc. After easily defeating Stinger, the Deep Sea King then goes after an A-Class hero, Lightning Max. Lightning Max attempts to attack the Deep Sea King, but to no effect, the Deep Sea King then attacks him, sending him flying across the street into another building, which then begins to collapse. The Deep Sea King gives chase and shows up just as Lightning Max recovers himself, Lightning Max then throws a powerful kick at Sea King, which doesn't do anything. The Deep Sea King then attacks him, sending him flying out of the building onto the street below. The building is about to fall on Lightning Max, but he is saved by S-Class hero Puri-Puri-Prisoner, who shows up with Sonic, the both of them having escaped from jail.
Puri-Puri-Prisoner then challenges the Deep Sea King to a fight, and powers himself up to "half power," which causes his sweater to rip, infuriating him. The Deep Sea King then attacks him with a devastating blow to the face, which Puri-Puri-Prisoner immediately returns, followed by an uppercut to the chest that sends Deep Sea King flying, but for the most part he remains unharmed. Puri-Puri-Prisoner is left damaged and off balance from the short skirmish and decides to go full power by "transforming," causing his muscles to expand and his clothes to rip off. Puri-Puri-Prisoner jumps forward and throws a chain punch, which is completely blocked by Deep Sea King, who then returns with his own chain punch, ending with a kick that sends Puri-Puri-Prisoner flying off into the distance, crashing through a building.
Sonic then challenges the Deep Sea King to a fight, who then rushes forward and attempts to punch Sonic who easily dodges the punch. The Deep Sea King then attempts to attack Sonic several more times, with Sonic dodging the attacks and eventually landing a kick on the Deep Sea King's face. After landing the kick a snakelike thing appears in front of Sonic and attempts to bite him, but only manages to rip his shirt. The snakelike thing is actually a long Moray that is coming out of the Deep Sea King's mouth. Deep Sea King goes to attack with his Moray again, but Sonic dodges in close and smashes the Deep Sea King's mouth closed, causing him to bite off the Moray. The Deep Sea King then attempts to use a chain punch on Sonic, who easily dodges and jumps at the Deep Sea King, attacks him and lands on the roof of a nearby building, but when he looks back, the Deep Sea King is laughing. The Deep Sea King the launches himself at Sonic and crashes into the roof of the building, with Sonic barely being able to dodge in time.After dodging away from Deep Sea King's attack, Sonic jumps off to a different building, but before he has a chance to do anything, Deep Sea King shows up. Deep Sea King then reveals that after he'd left the sea his body had shrivelled up, but thanks to the rain, he is able to return to his true form. Sonic then attempts to run away, but Deep Sea King follows him and eventually catches him, and crushes him, or so it would seem. However, when Deep Sea King opens his hand only Sonic's clothes remain. Sonic then appears on a nearby roof naked, vowing that the next time the two would meet would be their last, after which he leaves. Deep Sea King then decides to head out again.
Sensing a large number of life forms in the distance, the Deep Sea King heads out and finds J-City's evacuation centre. The Deep Sea King then smashes his way through the wall of the structure with ease, but before he can do anything C-Class hero All Back-Man steps forward to attempt to negotiate with the Deep Sea King. The Deep Sea King is amused by the hero's attempts, stating that the only thing he really wants is to hear some really nice death screams. At this point, All Back-Man loses it, wets himself and is about to completely break down when the heroes Jet Nice Guy, Bunbunman, and Sneck step forward to help buy some time for higher level heroes to arrive.
Jet Nice Guy charges forward to attack but Deep Sea King quickly dispatches him. Sneck then orders the remaining heroes to attack on the count of three but before Sneck can finish the count Deep Sea King attacks, quickly defeating Bunbunman and All Back-Man with the first strike and Sneck, having dodged the first attack, is taken out by the second. Boasting over the fallen heroes, Deep Sea King is then met by an enraged Genos, who delivers a devastating blow to the Deep Sea King's face, launching him out of the shelter and through several buildings.
Furious, the Deep Sea King returns and catches Genos off guard with a destructive punch to the head whilst also holding onto Genos' arm, ripping it from his body. Genos, worried that he might not win, orders all of the remaining civilians to evacuate the shelter, but Deep Sea King exclaims that all humans are his prey and that none will escape. Deep Sea King is then met with a powerful kick from Genos but he is prepared for the attack and he simultaneously retaliates with a punch. The Deep Sea King and Genos then trade blows for some time until a little girl who was evacuating yells back to Genos, urging him to hang in there. Upon hearing this, an annoyed Deep Sea King spits acid at the child, stating that brats should keep quiet and melt away. Left with no other choice, Genos throws his body into the path of the acid spit, saving the little girl but damaging his body greatly. Taking advantage of this, the Deep Sea King grabs Genos by the head and throws him into a nearby wall and then quickly follows-up with a devastating punch that sends Genos through the wall and out onto the street.
Standing over a heavily damaged Genos, the Deep Sea King admonishes him for his selflessness, but goes on to praise him for managing to injure the Deep Sea King, despite the fact that the injury had already healed. Before the Deep Sea King could finish off Genos, he is attacked from behind by Mumen Rider. Though the attack had no effect, the Deep Sea King turns to meet this new challenger. Mumen Rider charges forward with a punch, but the Deep Sea King easily blocks it and then grabs Rider and proceeds to flail him around like a rag-doll. The Deep Sea King then tosses Rider away and, thinking the C-Class hero was defeated, turns back to Genos to deliver the final blow. However, before the Deep Sea King can do so, Mumen Rider is back on his feet, and, despite heavy injuries and knowing full well he can't do anything, attacks once more, only to be swatted away by an extremely annoyed Deep Sea King.
Fed up, at last, the Deep Sea King delivers one final blow to Mumen Rider, knocking him right into the arms of the newly arrived Saitama. Enraged by a comment from the confident Saitama, Deep Sea King delivers a blow to the back of Saitama's head, but it appears that the attack does little more than annoy the bald hero. The Deep Sea King comments on Saitama's impressive durability considering that all the other heroes before him fell so easily, but Sea King is infuriated when Saitama states that Deep Sea King's blow was just so damn weak. The Deep Sea King goes on to boast about his title as king of the sea, but is further annoyed when Saitama tries to rush his monologue. Deep Sea King unleashes a powerful blow, but is cut short by Saitama's own attack which blows a hole through the seafolk's body and creates a massive shockwave that stops the rain. The Deep Sea King then falls to the ground, defeated at last.
Even after his passing, Puri-Puri-Prisoner and Lightning Max's defeat to the Deep Sea King still serves as motivation for them to become stronger. Also losing to him is what made All Back-Man quit the Hero Association. The last of the seafolk Lord Great White proclaims himself the new seaking and attempts to avenge his comrades before being stopped by Saitama. After his and the Subterranean King's deaths the Ancient King attempts to take the surface for himself before being killed by Tatsumaki. At the Super Fight Tournament, Sneck reminiscences back to how the Deep Sea King was stronger than him, which motivated him to become stronger as well.
Appearances in other Media Edit
He makes a cameo appearance when talking about disaster levels. 
Abilities and PowersEdit
The Deep Sea King is an immensely powerful being, able to fight on par and defeat several S-Class heroes and S-Class level fighters. He also appears to be able to sense people's presence in every direction, even if distant. According to the Hero Association's ranking system, it would take the strength of ten A-Class heroes, or one S-Class hero to defeat him. However, as Puri-Puri-Prisoner (who is an S-Class hero) was no match for the Sea King, this may be inaccurate. On the other hand, Puri-Puri-Prisoner is at the lowest level of S-class, and his blows weren't designed to kill Deep Sea King.
Water Empowerment: When his body is hydrated enough his form changes to that of his real form. In this form, he is much larger and more monstrous. However, sufficiently strong attacks or long periods out of water cause him to exit this form.
- Augmented Strength: In this form he boasts greater strength, being able to smash through buildings with ease.
- Augmented Speed: In this form his speed increases greatly, as he is able to keep up with Sonic, one of the fastest characters in the series, with ease for a considerable amount of time.
Immense Strength: The Deep Sea King boasts an extreme amount of strength seen as how he was able to dispatch two A-Class heroes with minimum effort. In his weakened state he's able to greatly damage and send Puri-Puri-Prisoner, an S-Class hero, flying through a building a great distance away alongside other heroes such as Lightning Max, an A-class hero. He was even able to tear apart Genos's cybernetic body with relative ease as well. However, in his Dry Form he was shown to take many blows from Genos who only had one arm and was unable to land any decisive blows on the hero until he used his acid spit.
Immense Durability: The Deep Sea King has incredible physical might, being able to easily withstand the attacks of several heroes ranging from C-Class to S-Class with little damage despite them occurring one after another with little rest in between. In his weakened state, he is able to take the powerful strikes of S-Class hero, Puri-Puri-Prisoner, head on without taking much visible damage alongside the attacks of Sonic, an S-Class level villain and S-class hero, Genos. Even after having his Moray cut off, he showed no visible signs of pain. 
Immense Speed: The Deep Sea King boasts an exceptional amount of raw speed, seen when he was able to appear behind Lightning Max instantaneously, catching the A-Class hero off guard. He even managed to slightly guard himself against Sonic, one of the fastest characters of the series, though couldn't land a proper hit on the ninja until he entered his true form. Along with this, his Dry Form was shown to be about on par if not slightly below the level of Genos.
Regeneration: While shown to be highly resistant to attacks, the Deep Sea King is capable of recovering from his injuries at an extreme rate, as seen when an injury he received from Genos, an S-Class hero, healed while they were still fighting. However, this ability does have limits, as a powerful blow can kill him before he has the chance to regenerate. 
Acid Spit: The Deep Sea King can shoot dangerous spit from his mouth that is extremely acidic, as it melted Genos' metallic body almost completely.
Master Hand-to-Hand Combatant: The Deep Sea King is an extremely skilled combatant, capable of defeating two S-Class heroes and seems to have lots of combat experience, as seen when he lectured Puri-Puri-Prisoner how to fight properly, by putting much more effort into attacking an opponent with more intent to kill. He also seems to have a preference for combo attacks, attacking his opponents mostly with a barrage of punches.
Body Moray (体内ウツボ, Tainai Utsubo): He can release a long eel-like creature from his mouth that he can use to bite and tear into opponents with. According to the Deep Sea King, the creature will not go away once it touched his enemies. Its full capabilities are unknown.
- The Deep Sea King is the third of many "kings" mentioned in the series, the others being the Subterranean King, the Beast King, the Ancient King (anime-only), the Sky King, the King of the Underworld, the Monster King, and the Forest King.
- The Deep Sea King is the first character to have had two variation points in the manga, showing his death at the hands of Saitama. One was Saitama destroying the road behind the Deep Sea King after he punched a hole through said Deep Sea King, and the second was the same punch through Deep Sea King except it created a small shockwave where the Deep Sea King was damaged.
- ONE stated Zombieman would have a difficult time defeating Deep Sea King.
- ONE stated that Sonic with weapons would've defeated dry form Deep Sea King.
- Murata stated he and Boros are his favorite monsters, due to the impact they've left on the series.
- Some speculate that Deep Sea King in true form is possibly on level Dragon due to being able to take on S-class heroes, although this has never been officially confirmed.