Philip II is the king of Macedonia and the father of Alexander in the anime Reign: The Conqueror. He rules alongside his wife Olympias, a priestess with ties to snake magic, and their son Alexander is born as his heir. As ruler of Macedonia, Philip leads his kingdom into war with Athens, supported by his chief advisers Attalus, Parmenion, and Antipater. During the campaign he is concerned about Alexander's absence from the battlefield, though Alexander and his cavalry arrive at the last moment and help secure victory by exploiting a break in the Athenian lines.

Philip is portrayed as a ruthless and cunning ruler who is determined to hold onto power and expand his empire. He is deeply invested in maintaining Macedonia as a major power and pursues that goal through military force and political maneuvering. He is also a capable military commander, regarded as a skilled strategist with an innovative approach to tactics and weaponry, including the use of the Macedonian phalanx formation. Beneath his ambition, however, he is a flawed and vulnerable figure. He struggles with alcoholism and an unhappy marriage, and he is haunted by his difficult relationship with his son.

His relationship with Alexander is central to his place in the story. Although he shows concern for his son during the war, he is later deceived by Attalus, who tricks him into believing that Olympias and Alexander are plotting against him. In response, Philip banishes Olympias and marries Attalus's daughter Eurydice. When Eurydice gives birth to a son, Philip plans to make the child his heir instead of Alexander. He holds a grand ceremony to present the new prince and commissions a massive golden statue of himself, declaring himself a god. During the ceremony the statue crumbles, and a guard who has been hypnotized by Olympias assassinates Philip. Following his death, Alexander ascends to the throne and has Attalus executed.

Over the course of his appearances, Philip changes from a concerned father and conquering king into an increasingly suspicious and self-glorifying ruler. His decision to disinherit Alexander, his claim to divinity, and his assassination during the ceremony mark the end of his reign and clear the way for Alexander's rise to kingship. His actions continue to influence the story after his death, as the political situation he leaves behind helps shape Alexander's early rule and ambitions. His notable abilities lie chiefly in military leadership, strategic thinking, and the use of political marriages and court intrigue to strengthen his position, while his pride and susceptibility to manipulation ultimately contribute to his downfall.