The Raiders started out in Terran Space as a trading guild. They corrupted into a form of organized crime, then became a trading clan, with side-branches in smuggling, mercenary fighting, and occasional piracy. When they started running planetary-scale protection rackets, they got chased out of Terran Space. Rather than face aliens that are just as hi-tech, less rewarding, and (on average) morally tougher than humans, they went out to the Terraform Reach, where they had heard there were humans and the technology was lower.
It was, kinda. Koliot ships were superior in short-range speed and manoeverability, Koliot troops had superior arms and more psi tricks. Koliot comm-tech and telemetry was slightly better. But New Terraformers soon caught up, and were better in heavy weapons, long-range drives, organization (that is, they eventually unified, unlike the Raiders), patharchy, and numbers. The Koliot ships burned, one by one, and the Koliots themselves filtered away into the general population, here and there forming die-hard trouble spots, or changing the timbre of the underworld in certain localities. Meanwhile, the New Terraformers had formed an empire containing a third of the Reach.
Ethnically, the Koliots were a thorough mix, looking therefore vaguely Polynesian so far as any one description holds. Koliot society was gang-like and piratical, headed by "chiefs" controlling small fleets of ships.
In as much as there was any Koliot religion, it was ghost-worship closely associated with their thojos (shamanistic psychics). It was based at least as much on appeasement as on supplication.
The Koliot language is an Earthron-based thieves' cant, with clipped, simplified grammar and a slang-heavy vocabulary borrowing from thieves' cants of Blenari, English, Yiddish, and Arabic. Koliot is now a source of funky or dark slang.
A Koliot background can give dark chic, if dark chic is acceptable in your circles, e.g. among spacehands, criminal elements, the underclass, and anti-imperials.