Moreover, Aeschylus anachronistically and artificially injects Io, another victim of Zeus's violence and ancestor of Heracles, into Prometheus' story. Finally, just as Aeschylus gave Prometheus a key role in bringing Zeus to power, he also attributed to him secret knowledge that could lead to Zeus's downfall: Prometheus had been told by his mother Themis, who in the play is identified with Gaia (Earth), of a potential marriage that would produce a son who would overthrow Zeus. Fragmentary evidence indicates that Heracles, as in Hesiod, frees the Titan in the trilogy's second play, "Prometheus Unbound". It is apparently not until Prometheus reveals this secret of Zeus's potential downfall that the two reconcile in the final play, "Prometheus the Fire-Bringer" or "Prometheus Pyrphoros", a lost tragedy by Aeschylus.