One of the most shocking moments of the entire franchise comes when EDI and Mordin discover the truth about the Collectors. The strange race of deformed kidnappers are actually the Protheans. The Protheans are the thought-to-be-extinct race that created the Citadel and Mass Relay devices. It's revealed that the Citadel and Mass Relays are actually of Reaper technology, and the Protheans were just another race to be wiped out by the Reapers.
Or so we thought.
It turns out the Reapers enslaved the Protheans through indoctrination, twisting and modifying them into what the galaxy now knows as the Collectors.
