Alexios is Kassandra’s brother in Assassin’s Creed Odyssey.
Odyssey allows the player to choose either Kassandra or Alexios as the playable protagonist. Whichever character is chosen, the other becomes the sibling known as Deimos, a figure shaped by the Cult of Kosmos and the family’s violent history.
This means Alexios is Kassandra’s brother in the game’s family storyline, while “Deimos” is the title or identity used for the sibling aligned with the Cult. Players can therefore encounter Alexios as the protagonist or as Deimos, depending on their selection, which causes frequent confusion.
The game’s story also includes Myrrine, Nikolaos, and Stentor. Odyssey is set during the Peloponnesian War, but its family drama is fictionalized and interwoven with historical Greece. The canonical promotional material generally presents Kassandra as the central character, while the game still permits Alexios as the player choice.