Lord Boros, also addressed by his subordinates as Lord Boros, is the former leader of the Dark Matter Thieves, an interstellar criminal organization responsible for the destruction of A-City. He is a cyclopean humanoid alien with a slim build, lightly colored spiky hair, pointed ears adorned with multiple earrings, and crack-shaped markings covering most of his body, including his face. A second eye resides below his chest and moves in synchronization with his primary eye. Initially, he wears a full-body armor designed to suppress his immense power. When the armor is broken by Saitama's punch, his body becomes slightly more muscular, his skin darkens, scales and spikes emerge, and his markings begin to emit energy. In his ultimate Meteoric Burst form, his appearance changes drastically: his hair lengthens, his eye's sclera turns black, his body becomes engulfed in energy, and his markings revert to a dark color.

Boros was born with extraordinary supernatural abilities, including immense strength, speed, durability, energy projection, and regenerative capabilities that far surpass those of his own race. He attributes the foundation of his power to the harsh environment of his home planet. As a result of his unmatched power, he grew arrogant and prideful, yet also deeply bored. No opponent in his sector of the universe could challenge him, leading him to roam the cosmos in search of a worthy adversary. A prophet revealed to him that on a distant planet called Earth, he would finally find an opponent capable of fighting on equal terms. This prophecy motivated Boros to travel for twenty years to reach Earth.

His primary motivation is not conquest or destruction for its own sake but rather the pursuit of a thrilling battle that could stimulate his existence. He seeks an opponent who can match his power and give him the fulfilling fight he has always desired. When he finally confronts Saitama, he is exhilarated and acknowledges Saitama's strength multiple times, even calling him worth defeating.

In the story, Boros serves as the main antagonist of the Alien Conquerors arc. He leads his invasion fleet to Earth and engages in direct combat with Saitama. Despite his overwhelming power, he is ultimately defeated after a prolonged and destructive battle that showcases the full extent of his abilities. His role highlights the thematic parallel between himself and Saitama, as both are beings who have become so powerful that they struggle to find meaning in battle.

Boros has few personal relationships of note. His subordinates revere him and address him as Lord Boros, but he does not appear to share deep bonds with them. His most significant relationship is with Saitama, who becomes the opponent he has been seeking for years. The prophet who gave him the prophecy is also a key figure in his journey, though they do not interact directly.

Throughout his brief appearance, Boros undergoes a clear arc. He begins as a conqueror driven by boredom, transitions into an excited and fully engaged combatant, and ultimately accepts his defeat with a sense of satisfaction. His final moments show a degree of respect for Saitama, as he acknowledges the hero's strength and appears content with having finally found a worthy opponent.

Boros possesses a range of notable abilities. His physical strength allows him to create shockwaves with his punches, disperse smoke clouds covering his enormous spaceship with a single blow, and launch Saitama to the moon, though this feat strains his body. His durability enables him to withstand multiple normal punches from Saitama, including the Consecutive Normal Punches attack, and remain conscious. He can enhance his speed and power through energy projection, and his regeneration allows him to instantly regrow lost limbs and even reassemble his body after being shattered into pieces. His signature techniques include Meteoric Burst, which unleashes his latent energy to dramatically increase his speed and strength at the cost of stamina, and Collapsing Star Roaring Cannon, his ultimate attack that releases all of his energy at once with the power to destroy the planet. However, after using this final technique, his regeneration ceases and he can no longer recover, leading to his defeat.