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 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 — quarians that have never left the Migrant Fleet due to illness, importance to the fleet, or disability. One of their current interests is in healthy human biotics. No one knows what happens to the individuals concerned after the exchange is completed.
Once at the base, the abductees were stored in organic pods.
Periodically, they would be broken down into raw genetic material which
was pumped through tubes to the centre of the Collector base and used to
construct the Human-Reaper. EDI
suggested that the Collectors were 'facilitating Reaper reproduction'
by constructing a new Reaper, and also estimated that the Collectors
would have to gather millions of humans in order to complete it. EDI
also speculated that any Reaper is built to resemble the race used to
create it, and that the Reapers had unsuccessfully attempted to
construct a Reaper from Prothean raw material.
When Commander Shepard
discovered the Human-Reaper, it was an inactive larva, supported by
four tubes. These tubes funneled genetic material into the Reaper and
also served as supports. After Shepard's squad destroyed all four tubes,
the Human-Reaper fell into a pit to its apparent destruction. However,
it was able to activate itself and climb back up to engage Shepard and
the team. They proceeded to destroy the Human-Reaper once and for all by
damaging specific points on its armour."(wiki)
Sovereign is a gigantic starship of almost unimaginable power and sophistication. Commander Shepard originally believed Sovereign was a Reaper
vessel that Saren Arterius found and somehow reactivated, but discovers
Sovereign is in fact an actual Reaper, a fully sentient and extremely
which is why the geth obey its commands. They see Sovereign as the
pinnacle of AI evolution and worship it as a god. However, Sovereign
regards the geth as no more than tools to aid in the return of the
Reapers and is even insulted by the worship the geth "throw" at it, and
Saren as simply a useful slave.
A vanguard of the Reapers left behind to instigate their eventual return from dark space,
Sovereign has spent the last 50,000 years in a state of near-constant
hibernation, waking periodically to assess the evolution of organic
races. It was the duty of the starship to bring about the next
revolution of the cycle, and serve as the harbinger for the return of
its kind by sending a signal to the keepers on the Citadel. This would make the keepers open the Citadel relay, a mass relay that leads to dark space, and usher the Reapers through.
Sovereign is also able to control organic life through the process of indoctrination.
A subtle field or signal surrounds the Reaper, gradually affecting the
organic's mind until they are little more than a shell of their former
self, bent on doing Sovereign's will. Sovereign has nothing but contempt
for any lesser beings, seeing them as fleeting and temporary, whereas
the Reapers are eternal. It also seemed angered by the attempts of
organic life to defend their claim to the Citadel, claiming "this
station is mine." (wiki)
Yahg from the game Mass Effect 2 - Lair of the Shadow Broker
The Shadow Broker is an individual at
the head of an expansive organization which trades in information,
always selling to the highest bidder. The Shadow Broker appears to be
highly competent at its trade: all secrets that are bought and sold
never allow one customer of the Broker to gain a significant advantage,
forcing the customers to continue trading information to avoid becoming
disadvantaged, allowing the Broker to remain in business.
In 2183, the Shadow Broker's identity was unknown; the Broker always operates through an agent. Barla Von refers to the Broker as "he" for convenience's sake, but tells Commander Shepard
that he believes the Shadow Broker is a group of individuals: it does
not seem possible for a single individual to monitor all of the
available information and have such a wide sphere of influence.
The Shadow Broker was part of the reason Tali came to the Citadel: the data file she had proving Saren Arterius
had gone rogue put her in danger, but was too valuable to waste. She
wanted to trade the information for a safe place to hide, so Dr. Chloe Michel put her in touch with the club owner Fist,
who worked for the Broker. However, unknown to her, Fist had changed
his allegiances to Saren. The Broker was furious at this treachery,
hiring Wrex to assassinate Fist... (more at wiki)