Quarian
The quarians are a nomadic species of humanoid aliens in Mass Effect who are known for their skills with technology and synthetic intelligence.
History
The quarians are responsible for creating the geth, originally intended as a non-sapient artificial work force. However, the geth slowly achieved sapience. Fearing revolt by the geth, the quarians preemptively tried to shut down all geth. This attempt failed, and caused the geth rebellion that the quarians were trying to avert. After a brutal war, the quarians were driven from their homeworld, Rannoch, and their major colonies.
The quarians now wander through the galaxy in the massive Migrant Fleet, either seeking a suitable new homeworld or a method to defeat the geth once and for all.
Attributes
The conditions of the native homeworld they evolved on and the artificially sterile environment of the fleet has left the quarian immune system extremely weak. They must wear environmentally sealed suits at all times, for any foreign microbe can cause intense illness and possible death in a quarian.