The Protheans were a race of humanoids who shepherded many of the modern Citadel races.
Biology[]
The Protheans had a standard body plan by Citadel standards, two arms, two legs, one head, but they had the distinction of quadrilocular vision, though their exact diet is unknown, it can best to be assumed they where predators as according to the last member of the species, in his time, Hanar where typically eaten fried, and Salarian liver was a delicacy.
Their species had a kind advanced mental ability, being able to share thoughts and memories, even with members of different species, this ability can allow them to sense what happened in a certain location, and this presumably was developed either naturally or via genetic engineering, and similar to most other species who came after them, some of their race had naturally occurring Eezo nodules throughout their bodies, allowing them to create small localized mass effect fields.
History[]
The Protheans at earliest, began their empire around Earth year 68,000BC, learning the secrets of mass effect physics from Inusannon ruins, and developing FTL Travel, discovering the mass relay network, and discovering the Citadel, early on, they began to know the threat of a mechanical intelligence, and they began granting other Sapient organics the "option" to join their empire and fight against the coming danger, eventually, the mechas did attack, and the empire did defeat them in the large Metacon War.
In the time following the war, the Protheans began observing many of the primitive species, Humans, Asari, Turians, Quarians, Salarians and Hanar, and they planned to eventually intigrate them into their empire, when the time was right.
Around the Earth year 48,000 BC, the Reapers returned to the galaxy, and they where wiped out, almost as quickly as they rose to power, when the Reapers where done with the Protheans, the genetically bastardized them into the horrible servant race, known as the Collectors, who now dwell on a planet near the Galactic Core, only accessible via the Omega 4 Mass Relay.