The Collectors are an enigmatic race that live beyond the Omega 4 Relay, a mass relay within the same system as Omega, in the Terminus Systems. They are rarely seen in the Terminus itself, let alone Citadel space, and are generally regarded as a myth by Citadel citizens. Definite sightings of Collectors have been made on Omega every few centuries.
They are most well-known for their odd trade requests for which they offer new technologies, often of a startling level of advancement. Their requests usually involve the trade of living beings in odd numbers and varieties, such as two dozen left-handed salarians, sixteen sets of batarian twins, a krogan born of parents from feuding clans, or two dozen "pure" quarians who have never left the Migrant Fleet due to illness, importance to the fleet, or disability.