While monitoring outgoing transmissions sent by the mysterious leader of the Collectors to his minions on the battlefield, Cerberus intelligence experts also intercepted incoming transmissions. The signals were encrypted commands sent to the Collector General from a source outside the galaxy. This directing intelligence is likely the Reaper that refers toitself as "Harbinger".
This indicates that the Collector General, previously thought of as a puppeteer-like figure, was essentially a mere conduit through which Harbinger mobilized the Collectors' mission to protect and nurture an embryonic Reaper by providing it a steady supply of humans. In this way, the Collectors allowed the proto-Reaper to incorporate the human genome into its own construction, though why a Reaper would want such a thing is still unclear.