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.
Elpidios was born around 422 BCE, when Kassandra, Natakas, and Darius decided to stop running from the Order of the Ancients and settle in Dyme, Achaia. Natakas and Kassandra married and bought a house on the cliffs above Dyme. When the Order arrived in full force to finally defeat them, Natakas was killed and Elpidios was captured, much to the dismay of Kassandra. Kassandra followed the Order ot Messenia and eventually hunted down Amorges with the help of Darius. Before dying to Darius hidden blade, Amorges revealed the location of Elpidios. He was being raised and nurtured by the son of Artaxerxes I of Persia on an island south of Messenia .
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.