Olympias is the mother of Alexander and the queen consort of Macedonia in the anime Reign: The Conqueror. She is introduced as a deeply supernatural figure, a priestess and snake witch whose union with King Philip II produces Alexander, the child she has prophesied will grow into the destroyer of the world. The series draws on the historical Olympias, a Greek princess of Epirus, daughter of King Neoptolemus I, who became the fourth wife of Philip II, but it amplifies her mystical qualities considerably. Her character is connected to serpents and divine forces, and she is shown entangled with a god in the form of a gigantic snake in connection with Alexander's birth, establishing her as someone who moves between the mortal court and the supernatural realm.

In terms of personality, Olympias is portrayed as secretive, formidable, and relentless in guarding her son's future. She is not presented as a conventional nurturing mother but as a figure of dark ritual and quiet menace, commanding fear and suspicion among those around her. Her personality is shaped by her absolute commitment to Alexander and her belief in the prophecy surrounding him. When her position at court comes under threat, she responds with calculated cruelty rather than passivity.

Her central motivation is securing Alexander's path to the throne. This drive defines her role in the early story. After the adviser Attalus convinces Philip that Olympias and Alexander are plotting against him, Philip banishes her and marries Attalus's daughter Eurydice, who gives birth to a son intended to replace Alexander as heir. Olympias answers by hypnotizing a guard who assassinates Philip during a grand ceremony, and it is implied that she then drives Eurydice into madness and kills both Eurydice and her infant child, clearing the succession for Alexander and enabling him to ascend as king.

Within the larger narrative, Olympias serves as both a cause of events and a lingering presence. Her prophecy that Alexander will destroy the world is later revealed as a secret known to figures such as Parmenion, giving her influence that extends far beyond the Macedonian court. During a battle, the soldier Philotas experiences a vision of Olympias summoning demons, which links her to the supernatural currents of the story even when she is no longer physically present. Her key relationships reflect her role as a catalyst: with Alexander she is the source of his destiny and his most determined protector; with Philip her marriage erodes into rivalry and ends in his assassination; with Attalus and Eurydice she is a remorseless enemy.

Olympias's notable abilities include hypnotism, which she uses to control a guard and kill the king, apparent command over serpents and demonic forces, and prophetic sight, since her declaration about Alexander's destiny frames the entire story. While she appears most prominently in the opening stretch of the series, her actions determine the political order that Alexander inherits, and her supernatural associations keep her presence alive in the story's darker moments. Overall, she is characterized as a queen mother whose fierce devotion to her son takes the form of ruthless, mystically charged intervention in the affairs of the Macedonian court.