He is voiced by Leo Fabian.
Killer is a muscular man with light-colored skin and long blonde hair. He wears a blue and white colored mask with multiple holes embedded in it. Pre-time skip, he wears a polka-dotted long-sleeve shirt and a blue pants. Post-time skip he wears a blue short-sleeve shirt, blue pants with a sash around it, large gloves around his arm, and dark-colored shoes.
Since becoming Kamazo, Killer does not wears a mask revealing his face with almond-shaped eyes, a pointed nose, and a dark colored lips. He constantly sports a smile on his face as a result from eating a SMILE fruit. He also wears dark-colored robes instead of the shirt and pants he would wear when he was a pirate.
Unlike Eustass Kid who can be temperamental, Killer is revealed to be calm and relaxed in most of his appearances. He does not speak too often and is loyal to his captain, Kid, and the pirate crew. Killer is more pragmatic than his captain by how he would try to break up a dispute Kid had with an alliance member. Despite his calm temperament, Killer like his captain is shown to be extremely violent by how he participated in attacking and crucifying pirates in the New World. Like his captain and his crew, Killer is shown to be homicidal given his reputation for causing violence along with his captain. Despite his collected and pragmatic behavior he have shown, Killer is shown to be shocked when Kaido crash-land on their pirate alliance base.
After undergoing changes from his time in Wano, Killer as Kamazo shows that he is brutal and violent. He has no qualms in attempting to murder a woman and a child, Hiyori and Toko, on the orders of Orochi. Kamazo shows that he is arrogant and believes that he is a strong fighter. He is willing to spare other people if they do not interfere in his mission, but he will try to kill them if they try to get in his way such as attempting to kill Hiyori for protecting Toko or attempting to kill Zoro for protecting Hiyori and Toko.
After eating the SMILE fruit, Killer can only laugh and smile. Killer is shown tearing up from laughing because according to Kid, Killer hated his own laughter to the point he wears a mask to hide his face and stopped laughing.
As the right-hand to Eustass Kid, Killer is known to be a strong fighter within the Kid Pirates. He is shown to have fast reflexes and a fast reaction time. Killer wields sharp blades that he uses when he faces his opponents.
When Killer fights Zoro in Wano as Kamazo, he is shown to be a challenging fighter in battle. He wields two large scythes that allows him to strike down his targets in an instant. He is able to fight on the same level as Roronoa Zoro, an experienced swordsman, and is able to injure him. Killer's fast reflexes and speed in battle makes it hard for his opponent to hit him.
When he was younger, Killer would wear a mask because he did not like his own laughter. He would attack anyone who made fun of his laughter and chose to stop laughing as a result. At some point, Kiler joined the Kid Pirates as Eustass Kid's right-hand man and would gain a large bounty for his crimes against society. For his crimes, Killer's bounty reached 160,000,000 berries.
Killer appears with his pirate crew on Sabaody Archipelago where they plan to go the New World afterwards. Killer and Kid manages to see the other supernova pirates. Killer and Kid later watch and witness the an auctioning of people at a auctioning house that was operated by Doflamingo. Killer and Kid also witness Luffy punching a Celestial Dragon. After Luffy's attack, the marines begin to assemble near the auction house. Despite the chaos, Killer and Kid manages to make it off the island without getting captured by Kizaru, Kuma, or the marines.
Killer and his crew manages to witness the conclusion of the Marineford War from afar on their ship. Killer and his crew manages to make it to the new world. Many days after the Marineford War, the Kid Pirates attacks a pirate crew by crucifying them and Killer is present when Kid makes an example out of pirates he considers weak in the new world.
During the time skip, the Kid Pirates have journeyed to Big Mom's territory and faced off against her forces until they had to leave. They also attack some of her ships. At some point, Kid ends up losing his arm when he encounters the Red Hair Pirates. Kid and Killer also gets into an alliance with Scratchmen Apoo and Basil Hawkins in order to work together to against Shanks, the leader of the Red Hair Pirates. Because of his actions in the new world, Killer's bounty raised to 200,000,000 berries.
Killer and Kid are seen talking among one another with Apoo and Hawkins in their alliance. Killer ends up breaking up a dispute that occurred between his captain and Apoo Scratchmen because of the mess in one of the rooms. Killer and his captain also witness Luffy defeating Caesar in a live broadcasting video.
Moments later, Killer and his allies hear a loud crash in their alliance headquarters. Killer and the other alliance members are shocked to see Kaido appear in front of them.
After Kaido crash-lands on their island, the alliance breaks up with Hawkins and Apoo joining Kaido's side and Eustass Kid getting severely beatened by Kaido and imprisoned. Killer along with Kid and Hawkins makes it to Wano Country. At some point under unknown circumstances, Killer eats a SMILE devil fruit which caused him to lose the ability to express anger and sorrow. He takes on the alias Kamazo the Manslayer. Killer gains a reputation in Wano Country for killing multiple people in the Flower Capital. However, it is revealed that he works under Kurozumi Orochi as an assassin who would go after people the latter stood against.
After the incident at the banquet, Orochi sends Killer to go after Toko for accidentally laughing at him. Killer pursues Toko who was protected by Hiyori all the way to the Ringo region. Killer is close to killing Toko and Hiyori until Zoro prevents him from cutting them down. Killer introduces himself to Zoro and tells him about his mission. He warns Zoro to get out of his way but the latter refuses and the two gets into battle. As they fight, Zoro is able to keep up with Killer until Gyukimaru attempts to attack Zoro for being distracted. As a result, Killer strikes Zoro near the chest with his scythe. Zoro immediately regains composure from the blow and defeats Kamazo by using one of Killer's scythes and two of his own swords in a powerful attack.
Since he fail to complete the task he was given, Killer was taken by the Beasts Pirates to Udon Prison along with his captain, Eustass Kid, (whom escaped from Udon prison) earlier. Kid wants to know what Kaido and Orochi did to Killer to make him smile and laugh all the time but Killer begins to tear up as he continues to laughs. Queen have both Killer and Kid tortured by attempting to drown them.
When Big Mom was swinging Queen around, Killer and Kid were saved from drowning when Queen crashed into the contraption holding them and knocked them out of the water. Raizo gives Kid the keys and he manages to unchain Killer and himself. Kid refuses Luffy's offer to be his ally and breaks out of Udon prison with Killer.
- Killer and Roronoa Zoro are the only pirates who are regarded as supernovas despite not being pirate captains.
- It has been 439 chapters since Killer has been introduced (in Chapter 498) until his face is finally revealed in Chapter 937.
- A silhouette of his face was seen in Chapter 926 when the Wano townsfolk talks about Kamazo the Manslayer.