The Gatherers were Acamarian marauders who lived in semi-autonomous nomadic bands and survived off piracy. Unlike other Acamarians, they maintained their clan identities and practiced more elaborate facial tattooing and/or scarification.
In the 2260s, generations of brutal clan warfare on Acamar III was coming to an end. However, a number of individuals refused to accept the nascent peace and left the planet, becoming the Gatherers. Over the next century, the Acamarian government made several unsuccessful attempts to bring the Gatherers back into the fold, including in 2348.
The Gatherers had raided several outposts in the Acamar system and neighboring areas over their time off-world. They also raided an Acamarian outpost, Tezber. They established their own Gatherer outposts to store their equipment and maintain camps. They had amassed a mixed collection of equipment including Artonian lasers, Tonkian homing beacons, Regalian phaser rifles and Noranium alloy scrap metal. They also stole a Federation reactor.
In 2366, they had expanded their raids to include Federation outposts and trade routes, which got their attention. Captain Jean-Luc Picard decided to encourage another attempt at reconciliation by the Sovereign Marouk. Negotiations between Marouk and Gatherer leader Chorgan were fruitless at first. But ultimately an assassination attempt on Chorgan by Yuta, Marouk's servant and a member of a rival clan, exposed the poisonous legacy of old hatreds and effected a breakthrough. The Gatherers agreed to a truce and began their reintegration into Acamarian society. (TNG: "The Vengeance Factor")