Nomadic survivors of a civilization nearly destroyed by the Borg, left desperate for energy and bitterly hostile toward former drones.
Most of the Caatati were assimilated by the Borg, and the small remnant that survived lives aboard aging ships, short of power, food and supplies. Much of their culture and technology was lost to the Collective, and they resent anyone tied to the Borg.
In Day of Honor, a Caatati ship led by Lumas seized Voyager's ejected warp core and demanded supplies and the surrender of Seven of Nine. Seven instead built a thorium generator to give them the energy they needed, and they returned the core, while Torres and Paris drifted in space suits awaiting rescue.