Cerberus
Immediately following the First Contact War, an anonymous extranet manifesto warned that an alien attempt at human genocide was inevitable. The manifesto called for an army - a Cerberus to guard against invasion through the Charon relay.
Derided as "survivalist rhetoric written by an illusive man", the manifesto and its anonymous author soon fell off the media radar. But in 2165, terrorists stole antimatter from the SSV Geneva, the sole figure arrested named his sponsor "Cerberus". Throughout the 2160s and 2170s, alleged Cerberus agents assassinated politicians, sabotaged starships bearing eezo, and conducted nightmarish experiments on aliens and humans. Denounced as human-supremacist, Cerberus calls itself human-survivalist.
Counterterror experts speculate Cerberus may have changed leadership with it recent shift to stockpiling ships, agents, and weapons. Whether "he", "she", or "they", the Illusive Man hides his finances behind shell companies. Few doubt he will kill anyone attempting to expose him.
Cerberus: The Illusive Man
The reclusive tycoon calling himself the Illusive Man is a human nationalist focused on advancing human interests, whatever the cost to non-humans. The Citadel Council regards him as a fanatic posing a serious threat to galactic security.
A mysterious maverick to say the least, the Illusive Man heads the Cerberus network. Dubbed "the illusive empire" by investigators, Cerberus is an allegedly untraceable syndicate of private intelligence agencies, biotics laboratories, engineering and scientific research teams, and lucrative front companies.
Branded a terrorist and seditionist organization by authorities, Cerberus is the only human power base other than the Terra Firma Party strong enough to embarrass - if not threaten - the Council and its human representatives.
Mercenaries: Blue Suns
Founded by notorious batarian slaver Solem Dal'serah, the Blue Suns began as a Skyllian Verge protection racket providing genuine protection from slavers and pirates. Eventually captured by the Systems Alliance Navy, Dal'serah beat almost two dozen charges to be convicted on a single count of conspiracy. The slaver benefited from the tutelage of cellmate and brilliant con artist Bernard "Legits" Ledger. Upon release five years later, Del'serah incorporated Blue Suns as a legal security agency.
Today, the Blue Suns boast a galaxy-wide force of batarians, turians, humans, and asari. Each deployment is backed by a logistics corps selling everything from heavy weapons to shaving cream. Despite claims that Blue Suns sell its captives as slaves, no Blue Suns employee has ever been convicted on such charges.
Many Blue Suns members sport the company logo in tattoo form, removed during assignments and reapplied at mission-end.
Mercenaries: Eclipse
Brainchild of asari commando Jona Sederis, Eclipse was incorporated as a "proactive" security company. Influenced by asari and salarian military doctrine, Eclipse specializes in sabotage, assassination, and personal and organizational security. Although Citadel governments regard the corporation with suspicion, it's embraced in the Skyllian Verge and Terminus Systems.
Early on, Sederis sought government contracts to establish market share against the better-established Blue Suns. Her agency scored a galactic PR coup by retaking several space stations captured by the Anhur People's Liberation Army and neutralizing its leaders, a victory Eclipse's marketing department never ceases trumpeting.
Based on Omega Station, Eclipse controls nearly 20% of the asteroid's real estate. Its services range from mech repair to open warfare, although assassination is reserved for meeting wider, longer-term company goals (for instance, preemptive strikes against pirates rather than murdering spouses for insurance money.) Despite numerous reports, Eclipse denies sabotaging or kidnapping business rivals.
Mercenaries: The Blood Pack
Originally a small Terminus Systems vorcha gang, the Blood Pack was transformed into a legion by visionary krogan battlemaster Ganar Wrang. Exiled for striking a female in anger, Wrang obsessed over reclaiming his lost status.
Leading the vorcha pack as a pirate crew, Wrang cultivated recruits and infamy for a decade before incorporating his fighters as a security company across the Skyllian Verge. His notoriety ensured his initial public offering for investors made him rich beyond most krogan's dreams, Wrang returned triumphantly to his clan, rallying elders, krogan hordes, and their firepower and biotic support toward professional violence in the Terminus Systems.
Banned from Citadel space, the Blood Pack bribes its way through spaceports into armed conflicts across the galaxy. Priding themselves for accepting otherwise untouchable contracts, the Blood Pack rejects bodyguarding and security in favor of cases requiring minimal oversight and maximal violence.