Melzargard is a fictional character from the Japanese anime and manga series One Punch Man. He is an extraterrestrial being and serves as one of the three most powerful lieutenants, or "upper-level combatants," of the Dark Matter Thieves, a notorious group of alien pirates led by the tyrant Boros. His designated disaster level, a metric used by the Hero Association to gauge the threat of monsters, is Dragon, indicating a threat capable of destroying multiple cities.

In terms of background, Melzargard is an alien whose origins are not detailed in the story. What is known is that he has been part of Boros's crew for a very long time. During his final battle, he mentions that his five distinct personalities have coexisted for over a hundred years, suggesting his age is at least a century, if not far older. His primary role within the Dark Matter Thieves is as a guardian, tasked with patrolling and defending the exterior of their massive spacecraft, serving as the first line of defense against any attackers.

Melzargard's appearance is highly unusual and inhuman. He is a large, muscular humanoid figure with pale gray skin and red eyes. His most defining physical trait is his possession of five heads, each with its own distinct face and expression. These heads are not merely cosmetic; each one houses an independent personality and a small, marble-like core that is the true source of its life. His body is not a fixed form; he has complete control over his cellular structure, allowing him to shapeshift at will. He can stretch his limbs, create additional body parts, morph his arms into deadly weapons like hammers and blades, or sprout wings to achieve flight.

The personality of Melzargard is a complex and unique collection of five separate consciousnesses. These heads constantly talk to each other, comment on the situation, and offer suggestions. One head might speak in broken, simple language, another could be analytical and observant, a third might be violent and bloodthirsty, while another may be more decisive and take the lead. A further head is often shown praising the ideas of the others, creating a strange internal dynamic. Despite their individual quirks, all five share a common trait: a sadistic joy in combat and an arrogant confidence in their own power and immortality, often taunting their opponents. Interestingly, as heads are destroyed in battle, the remaining ones seem to become more articulate and intelligent, implying that their cognitive faculties are distributed across the five cores. His primary motivation appears to be serving his master, Boros, and successfully completing his mission of planetary subjugation. He takes pride in his strength and enjoys testing it against worthy opponents, expressing excitement when he discovers that Earth has beings capable of fighting him.

Melzargard's most notable abilities revolve around his incredible regenerative power, which is directly tied to his five cores. As long as even one of these cores remains intact, he can regenerate from almost any wound, no matter how severe. This includes regrowing entire limbs, heads, or even reconstituting his body after being blown to pieces. This effectively makes him immortal unless all five cores are destroyed. To further protect this weakness, the cores can move freely throughout his body, making them nearly impossible to locate when his form is intact. His other primary ability is shapeshifting, which he uses both for offense and utility. He can harden his body into powerful striking implements, with a single hammer-like blow being strong enough to tear off the arm of Iaian, a highly ranked A-Class hero. He can also split his body into five separate, independently acting units, each containing one head and one core, allowing him to fight multiple opponents simultaneously or cover more ground. Conversely, he can merge all five bodies together into a "combined" form that is stated to be dramatically stronger, faster, and more intelligent than his individual parts.

In the story of One Punch Man, Melzargard serves as a formidable secondary antagonist during the Alien Conquerors arc. He first appears in the skies over City A, where he immediately demonstrates his power by effortlessly slaughtering the Sky King and his entire Skyfolk army in a single, casual strike. He then descends to the city and engages the heroes. He quickly overwhelms the A-Class hero Iaian, severing his left arm with a single blow. This forces the intervention of four S-Class heroes: Atomic Samurai, Bang (Silver Fang), Metal Bat, and Puri-Puri Prisoner. The four heroes attack Melzargard together, but his regeneration allows him to withstand their combined assault. He even manages to fight back and contact his ally Geryuganshoop on the mothership, requesting backup firepower. The tide of the battle turns when Metal Bat, during the chaos of smashing one of Melzargard's separated heads, notices a small, hard marble inside the creature's head. He crushes it, and that specific head dies permanently, unable to regenerate. Realizing this is the core weakness, Metal Bat alerts the other heroes. They shift their strategy to focus on crushing the marbles, and one by one, they destroy Melzargard's cores. In a final desperate move, he calls for the mothership to fire its cannons on his position, hoping to kill the heroes. However, the psychic S-Class hero Tatsumaki easily deflects the bombardment. With only one core remaining, Melzargard is cornered. As he attempts to regenerate his final head, Bang catches the exposed core and crushes it, ending the alien's life for good.

His key relationships are hierarchical. He is a loyal and powerful subordinate to Boros, the leader of the Dark Matter Thieves. He is a comrade-in-arms to Geryuganshoop and Groribas, the other two top lieutenants, and he communicates with them during the invasion. He holds no particular relationship with the heroes of Earth beyond that of an invader to his victims, though he does develop a sense of respect for their persistence and strength during his final battle. Melzargard is notable for being the only high-ranking member of Boros's crew who does not encounter the protagonist, Saitama. This unique distinction allows him to have an extended and detailed fight scene against multiple heroes, showcasing his powers and abilities far more comprehensively than his allies, who are defeated by Saitama in a single punch. His development is minimal, as he is a static villain, but his defeat represents a significant victory for the S-Class heroes, demonstrating that even a Dragon-level threat can be overcome with teamwork, tactical thinking, and the exploitation of a hidden weakness.