Leonidas I appears as a historical character in Assassin's Creed Odyssey.
Odyssey opens in 480 BC with the Battle of Thermopylae, where Leonidas leads Spartan forces against the Persian army. The opening sequence establishes the protagonist's family history and frames the game within the wider conflict between Athens and Sparta during the Peloponnesian War.
Leonidas is not the game's main playable character. Players control Kassandra or Alexios, descendants of Leonidas through the game's fictional family narrative. Other historical figures, including Pericles, Brasidas, and Socrates, also appear later. The game uses real events and people as a foundation but combines them with fictional characters, mythology, and the series' Isu storyline, so not every person or event shown should be treated as literal history.