Planet of origin: Unknown, relocated to Ba'Ku, a ringed planet in The Briar Patch, AKA Klach D'Kel Brakt, in the Milky Way, a region containing dangerous space matter including the remains of supernovae, false vacuum fluctuations, metaphasic radiation and at least two habitable planets, one of which was Ba'Ku.
The Ba'ku are a humanoid species almost indistinguishable from humans, which, in the early 21st century, developed a civilization capable on space travel as well as the means of building weapons of mass destruction which brought them to the brink of self-annihilation. A small, enlightened group of the Ba'ku people escaped the horror of their homeworld and found an isolated planet where they followed a simple way of life and prohibited themselves from using technology. The metaphasic radiation in the planet's rings caused their aging process to significantly decelerate, making them nearly immortal.
A younger generation, eager to explore the galaxy, rebelled against their elders. Unsuccessful, they were exiled in the late-23rd century and eventually became the Son'a people, a nomadic interstellar power, living under the direction of the Son'a Command. Narcissistic and materialistic, they put great values in metals and ores and raided inhabited worlds for these resources, often using slave labor. Without the regenerative effects of the Ba'ku homeworld's metaphasic radiation, they became infertile and worked heard ot retard their death by any possible means, including genetic manipulation and surgical techniques. Some sociologists attributed their aggressive behavior to desperation.
In 2375, First Contact between the Ba'ku and the Federation was established during a failed cultural observation mission, when a monitoring post was discovered on the planet. This came at a moment of tensions between the Ba'ku, the So'na, the two groups were reunited.
Source: Star Trek universe (Star Trek: Insurrection)