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As a result of his parentage, Elpidios had Spartan and Persian ancestry. His paternal grandfather was Darius, and his maternal great-grandfather was Leonidas I of Sparta. Elpidios would also become the ancestor of Amunet, one of the Hidden Ones' founders.
Deeming Elpidios' parents to be too dangerous for his upbringing, Amorges, the leader of the Order of Dominion, had Natakas killed and kidnapped Elpidios. Travelling to an island south of Messenia, he entrusted the baby to Darius II, the son of King Artaxerxes I of Persia who had been forcefully overthrown and exiled.
Elpidios was later handed over to Kassandra, who learned her child's whereabouts from Amorges before his death. Owing to her lineage as a Tainted One, Kassandra came to the conclusion that Elpidios would never be safe with her and thus made the decision to let Darius take away Elpidios somewhere safe.
- The name Elpidios (Ἐλπίδιος) is derived from the Greek word ἐλπῐ́ς (elpís), which means 'hope'. Elpidios subsequently means 'hope, hopeful'.
- If Alexios is chosen as the playable protagonist instead of Kassandra, he is placed as Elpidios' father while Natakas' sister Neema serves as his mother.