Leonidas I is the ancient Greek warrior ancestor of Assassin's Creed Odyssey's playable hero.
Odyssey opens with King Leonidas of Sparta fighting at the Battle of Thermopylae in 480 BCE. The main story then follows a later descendant, who can be played as either Kassandra or Alexios, during the Peloponnesian War.
Leonidas's spear is an important story object. It is connected to the Isu and to the protagonist's bloodline, although the playable hero is not Leonidas himself. The opening battle functions as a historical prologue before the game shifts to the fifth century BCE.
A common mistake is to identify Leonidas as Odyssey's main playable character. He is playable only in the opening sequence, whereas the chosen sibling remains the central protagonist for the main campaign.