The Dark King, also known as the Evil King, is a central antagonist in the story of Futari wa Pretty Cure Max Heart, having originated as the primary villain in the preceding series, Futari wa Pretty Cure. He is the formidable ruler of the Dotsuku Zone, also known as the Dusk Zone, a dark and desolate parallel world shrouded in mist and devoid of sunlight. In physical terms, he is depicted as an enormous, muscular entity with piercing red eyes, and in his appearances, he is often rendered using CGI, which sets him apart visually from other characters. His presence is literally chained to the center of his dark realm, hinting at a connection between his existence and the destructive nature of his home world.

In terms of personality, the Dark King is described as the most evil existence in his universe, driven by an insatiable love for destruction. However, this desire is not born of pure malice alone but from a critical weakness: the very Power of Destruction that he commands is slowly killing him from within. His primary motivation is therefore a desperate search for immortality. To achieve this, he seeks to acquire the Power of Creation, which he views as his rightful property, believing it will halt his self-destruction. This goal leads him to attack the Garden of Light and attempt to steal the seven Prism Stones, which are the vessels of the creative power he craves. He is notoriously impatient and ruthless towards his own servants, punishing failure without mercy. A stark example of his cold-hearted nature is when he kills his own strongest and most loyal henchman, Ilkubo, not for failing, but for succeeding too well and risking damage to the very Prism Stones he was trying to obtain.

The Dark King's role in the story of Max Heart is that of an overarching threat whose lingering influence drives the plot, even when he is not physically present. Following his defeat in the first series, it is revealed that he cannot be completely obliterated, as his existence is tied to that of the Queen of Light. In the finale of the original series, he shot out a final burst of dark energy that gravely wounded the Queen, leading to her fragmentation into the girl Hikari Kujou and the twelve Heartiels. For most of Max Heart, he is absent, but his potential resurrection is the central goal of the season's main villains, the Four Guardians: Circulas, Uraganos, Viblis, and their leader, Baldez. Their actions are all dedicated to reawakening their king by nurturing a mysterious young boy who is, in fact, the Dark King's reincarnated life force.

Key relationships define his legacy. His most important connection is with Baldez, the leader of the Four Guardians. Unlike his previous underlings, Baldez is not merely a servant but is revealed to be the Dark King's designated successor. In the climax of Max Heart, Baldez successfully revives the Dark King, who returns in a feral, non-speaking state. Baldez then physically fuses with the revived king, absorbing his powers and becoming the new Dark King, serving as the final and most powerful incarnation of the villain that the Pretty Cures must face. The other significant relationship is an indirect one with Hikari Kujou, who is the life force of the Queen of Light. The Dark King and the Queen are opposing forces, yet their existences are linked; the child born from the Dark King's life, a boy named Hikaru, is ultimately rescued from the darkness and raised by Hikari, bringing a sense of closure to the cycle of conflict.

In terms of development, the Dark King's arc spans two series. He begins as a present and active threat, is defeated, and then his lingering energy causes further problems. In Max Heart, he is less a character and more a force of nature, existing as a potentiality to be revived. His final fate is to be absorbed by Baldez, and this combined entity is ultimately destroyed for good by the power of Shiny Luminous, who merges with the Queen of Light. With his final death, the cycle ends, and his reincarnated life force, the boy Hikaru, is freed to live a normal life.

The Dark King possesses notable abilities befitting his status. His primary power is the Power of Destruction, a force that allows him to wreak immense havoc but paradoxically consumes his own body. He is capable of generating powerful minions, such as giving birth to the Seeds of Darkness after his first defeat. His immense size makes him a terrifying physical threat, and he can consume other beings, like the traitorous Seeds of Darkness, to absorb their power for his own benefit. Despite being mostly silent in Max Heart, where he is reduced to little more than a roaring beast, his sheer presence and the power he represents are enough to make him the ultimate obstacle for the series' heroes.