Kassandra is the Eagle Bearer protagonist canonically chosen for Assassin's Creed Odyssey.
Odyssey allows players to select Kassandra or Alexios as the playable character. Ubisoft has identified Kassandra as the canonical protagonist, while Alexios serves as the game's alternate playable character and appears in another role within the story.
The game takes place in Ancient Greece during the Peloponnesian War, beginning in 431 BCE. Kassandra is a mercenary whose journey involves family conflict, political factions, the Cult of Kosmos, and the wider legacy of the Isu.
Phoibe is a young character who helps Kassandra early in the story, and Aspasia is a major historical figure connected to Athens. Neither is the protagonist. The choice between Kassandra and Alexios is a gameplay option, but canon identifies Kassandra specifically.