Batarian

A race of four-eyed bipeds native to the world of Khar'shan, the Batarians are a disreputable species that chose to isolate itself from the rest of the galaxy. The Terminus Systems are infested with Batarian pirate gangs and slaving rings that competes with the pirate-based Kig-Yar, fueling the stereotype of the Batarian thug and continuing the feud existing between the both species since the start of the Human-Covenant War. It should be noted that these criminals do not represent average citizens, who are forbidden to leave Batarian space by their ubiquitous and paranoid government

Despite several disagreements with the Citadel and simmering hostility toward Humans, most batarians prefer profitable pursuits such as drug running and slave grabs to out-and-out warfare. They have a reputation for being shrewd businessmen and merchants, though in more lawless regions of the galaxy like Omega, negotiations with a Batarian are likely to be conducted at gunpoint.

The Ark and Reseeding
The Batarians were one of the many species indexed on the Ark by the Librarian as a part of the Conservation Measure. After the firing of the Halo Array, the Batarians returned to their homeworld of Khar'shan were they begun rebuilding their culture.

Development of Civilization and the Citadel
Centuries later, when the Batarians achieved spaceflight, they discovered concealed Forerunner ruins on Bira, a moon of Verush, that allowed them to develop spipspace travel. It is a Batarian point of pride that, since the ruins were damaged by earthquakes, they had less information to go on than other spacefaring races. The Citadel Council granted the Batarians an embassy on the Citadel centuries after the Elcor, approximately a century after the Batarians and Council had made first contact.

Despite being welcomed into the galactic community, Batarian aggression provoked several crises in galactic relations over the years. Sometime around 1785 CE, a Batarian fleet bombarded the Salarian colony world of Mannovai; in 1913, the Batarian Hegemony annexed the independent Asari colony of Esan; and in 2115, Citadel forces skirmished with Batarian forces on the planet Enael.

Human-Covenant War
During the Human-Covenant War, the Batarians used of the Covenant's lust for the deaths of humanity that they secretly started trading illegal weapons with the hegemony at outer rim territories, something which the Covenant's High Prophets acknowledged and tolerated, even at the cost of their supposed divine salvation. This role led many Kig-Yar pirates, a Covenant client species, to develop a harsh relationship with the Batarians, even greater than their hatred for the Unggoy.

Batarian-Human Agression
In the early 2553, Humans began to colonize the Skyllian Verge, a region the Batarians were already actively settling. The Batarians asked the Citadel Council to intervene and declare the Verge an area of "Batarian interest". When the Council refused, the Batarians closed their Citadel embassy and severed diplomatic and economic relations, becoming an inward-looking rogue state.

Money and weapons funneled from the Batarian government to criminal organizations led to many brutal raids on Human colonies in the Verge, such as Mindoir, culminating in the Skyllian Blitz of 2555, an attack on the Human capital of Elysium by batarian-funded pirates and slavers. In 2556, the Alliance retaliated with a crushing assault on the moon of Torfan with the forces of the Sword of Sanghelios, the newly galatic faction led by the Sangheili, who since the dissolution of the Covenant allied with their former enemies and nailed to peace, long used as a staging base by Batarian-backed criminals. In the aftermath, the Batarians retreated into their own systems, and were rarely seen in Citadel space.

In 2557, Batarian extremists hijack Asteroid X57 in order to use it against the Human colony of Terra Nova. Originally intending to only snatch X57's Human engineers and take them as slaves, the Batarians brutally executed them and decided to use the asteroid as a weapon. Balak, the ringleader, claimed this was the will of the "Batarian rebellion", and revenge for Human activities in the Traverse. However, some of his underlings, including Balak's second-in-command Charn, did not want to commit this act, having initially signed up thinking it would be just another slave raid. The attempted asteroid drop, which would have destroyed Terra Nova and killed millions of people, was thwarted by Commander Jane Shepard and the UNSC Infinity forces.

The Batarians found themselves in numerous dead ends as now their factions were being hunted down by the Citadel, the UNSC and several vengeful Kig-Yar factions who wished for themselves Batarian territory.

As the Batarian ambassador Jath'Amon attempted to negotiate a peace treaty between the Batarians and the Citadel Council in 2558, Batarian terrorists attempted to stop the meeting by unleashing a biological weapon. Fortunately for the Council, the terrorists, secretly led by Jath'Amon himself, were defeated by Jacob Taylor before they have a chance to use the weapon.

Biology
Batarians are an anthropoidal race like Humans and Asari. Their faces are covered with short, fine hairs that grow longer and thicker around the mouth. A flat stripe of ridged cartilage runs along the tops of their skulls and down the backs of their necks. They have ears pointy at the upper end, though on occasion along the edges as well. The part of their faces commonly associated with the nose among humans and asari is instead an inverted flat triangle symmetrically ridged vertically.

Their most distinctive physical feature is their four eyes, an uncommon trait among other sapient races. One pair is set wide in prominent bony sockets protruding from the corners of their face. The second set of eyes is smaller and closer together, set higher on the face, just beneath the middle of the forehead. The eyes are uniformly dark orbs, with no discernible irises or pupils.

Batarians exhibit a wide range of skin tones and colors. Most Batarians encountered through the galaxy have a dark brown hue with pale facial ridges. General Batarian complexions include reddish-brown, greenish, yellow-greenish to yellow-brownish, light brown, and teal.

Some Batarians possess striped colorations on their heads. Observed patterns include multiple chin stripes, a single strip running from the lower lip, or a thin dagger of color above the nose. These patterns are usually colored blue, black, or red, while the nose pattern is invariably red. At least one, Balak, has what appears to be a black and yellow striped pigmentation at the temples with light green facial ridges.

Source

 * Mass Effect Wiki