Olimpiade, a name more commonly rendered as Olympias in English-language materials, is the mother of Alexander and the wife of King Philip II of Macedonia in Reign: The Conqueror. She is presented as a priestess and a snake witch whose connection to the supernatural sets the tone for the series' fantastical treatment of Alexander's story. Her introduction is tied to an encounter with a divine being in the form of a gigantic serpent, an event that marks her as someone operating beyond ordinary mortal politics and that establishes the mystical circumstances surrounding Alexander's birth. Prior to his birth, she proclaimed that Alexander would grow up to destroy the world, a prophecy that hangs over the entire narrative and gives her maternal ambitions a distinctly ominous quality.

In terms of personality, Olimpiade is calculating, secretive, and ruthless. She is willing to use manipulation, dark rituals, and indirect violence to achieve her ends rather than confronting her enemies openly. Her devotion to Alexander is genuine in the sense that she works tirelessly to secure his position as heir to the throne, but her methods are cold and her influence unsettling. She does not appear to be motivated by personal glory; instead, her driving motivation is ensuring that Alexander ascends to power and that any threat to his claim is eliminated. Her actions are also guided by her belief in prophecy and fate, and she treats the supernatural forces she commands as tools to shape events in her son's favor.

Her role in the story is primarily that of a behind-the-scenes force who determines the course of the Macedonian succession. When the adviser Attalus tricks Philip into believing that Olimpiade and Alexander are plotting against him, Philip banishes her and marries Attalus's daughter Eurydice, who then bears a son intended to replace Alexander as heir. Olimpiade responds by orchestrating Philip's downfall: during a grand ceremony in which Philip declares himself a god, a hypnotized guard assassinates the king, and the event is tied directly to her influence. She is also implied to have driven Eurydice into madness and to have killed both Eurydice and her infant son, thereby removing every obstacle between Alexander and the throne. Beyond these concrete acts, she remains a spectral presence in the story, appearing in visions and dreams, such as a vision experienced by Philotas in which she summons demons, and a dream shared by Alexander about the wonders of the world.

Her most significant relationship is with Alexander. She is at once a protective mother and a figure connected to his destructive destiny, and the bond between them is complicated by the prophecy she herself declared. Her relationship with Philip is one of estrangement and mutual suspicion, ending with his death at the hands of an assassin under her control. Toward her political enemies, particularly Attalus and Eurydice, she shows no mercy. In terms of development, Olimpiade does not undergo a personal transformation over the course of the series; she functions more as an unchanging, enigmatic force whose early choices set the tragedy of Alexander's life in motion and whose presence lingers over his conquests.

Her notable abilities derive from her role as a snake witch and priestess. She has the power to hypnotize others, as seen when she takes control of a guard to carry out Philip's assassination, and her witchcraft is associated with serpents and demonic forces. She is also capable of prophetic declarations, as demonstrated by her early claim about Alexander's future, and her supernatural influence appears to reach across distances, manifesting in visions that others experience during moments of crisis. Within the story she is therefore not merely a political figure but an active supernatural agent whose magic is integral to the rise of Alexander.