Conde Milenario, whose name translates to the Millennium Earl and whose Noah name is Adam, stands as the primary antagonist and a being of immense age, having existed for more than seven thousand years. He is the patriarch of the Noah Family and the First Disciple of Noah, presenting himself as a grotesque caricature of a Victorian gentleman. In his usual Noah form, he is a large, rounded figure with sickly grey skin, dressed in a grand coat and top hat, with an enormous, fixed smile that never leaves his face even when he speaks or eats, and small spectacles that permanently hide his eyes. When he reveals his true human form, he appears as a handsome man in his late twenties or early thirties, with amber eyes, medium-length purple hair styled back, and a thinner, more refined version of his usual attire.

The personality of Conde Milenario is defined by a stark and compelling duality. On the surface, he consistently behaves as a cheerful, carefree, and flamboyant figure, often speaking in a cutesy or affectionate manner and ending his sentences with a heart symbol. This persona can make him seem almost friendly or eccentric, such as when he inexplicably produces a rooster costume or interacts gently with a young girl selling flowers, whom he buys flowers from. However, this joyful exterior masks a profoundly malicious and sadistic being who callously manipulates human grief for his own ends. He takes advantage of those mourning lost loved ones, tricking them into resurrecting the dead as Akuma, mechanical weapons that are forced to destroy the very person who summoned them. The true depth of his darker side surfaces in moments of extreme rage, such as when a significant portion of his plans is thwarted, or when he obsessively recalls past betrayals, revealing a face of madness and intense fury that contrasts sharply with his typical demeanor. Despite his immense power and destructive goals, he has shown glimmers of something resembling care, particularly toward other members of the Noah Family, with a notable closeness to Road.

His overarching motivation is to lead humanity to absolute destruction, mirroring the Great Flood from biblical times. To achieve this, he seeks to find and destroy the Heart of Innocence, the core of the very substance that opposes him. His role in the story is that of the ultimate antagonist, the orchestrator of the war between his Noah Family and the Black Order of Exorcists. He is the creator and master of the Akuma army, using these tragic creatures as his main force to eliminate humanity and fight the Exorcists.

His history is deeply entwined with the central mysteries of the narrative. Around thirty-five years before the main events, a Noah known as the Fourteenth, Nea Walker, betrayed the family and attempted to kill the Millennium Earl to take his position. The Earl was forced to kill Nea, an event that left him emotionally scarred and suffering from lingering pain. Later, when Nea's brother, Mana Walker, died, the Earl appeared before Mana's adoptive son, Allen Walker, and tricked him into trying to turn Mana into an Akuma. This act backfired when Allen's own Innocence activated, destroying the Akuma and revealing his potential as an Exorcist. The Earl chose to let the young Allen live, a decision he later questions, especially after learning that Allen is the reincarnation of the very Fourteenth who had betrayed him. This revelation shifts their relationship, as the Earl begins asking Allen to join the Noah Family, even while harboring an intense, unforgiving hatred for Mana Walker.

Conde Milenario's key relationships are central to his character. As the leader, he is the patriarch of the Noah Family, and while he can be fearsome, he also shows concern for them. His bond with Road Kamelot is particularly close, and he is known to help her with her tasks. His relationship with Allen Walker is the most complex, driven by Allen's connection to the Fourteenth, Nea, blurring the lines between enemy, potential ally, and a source of painful memories. His current development shows a being still not fully recovered from the trauma of Nea's betrayal, prone to sudden bouts of pain and weeping, and now confronted with a world where his past is returning to challenge him.

Conde Milenario possesses formidable abilities befitting his ancient and powerful status. His primary weapon is his living, talking umbrella named Lero, which he can transform into a sword that mirrors the Exorcist Allen Walker's own weapon, but with inverted colors. Beyond this, he has demonstrated the capacity to create massive explosions of Dark Matter, the substance that powers the Akuma and the Noah. As the creator of the Akuma, he exercises complete control over his demonic army, commanding them to do his bidding without question. He is a powerful sorcerer, having engaged in ancient battles against unknown opponents who wielded the Heart of Innocence itself, and is regarded as the most powerful of the Noah Disciples.