They were ruled by King Zornog. When General Sludd tried to usurp the throne of nearby Alzar, he tricked Alzarian heir Prince Plooz into running away to Sooma on a freighter; Plooz was later rescued by C-3PO and R2-D2.
Ten months after the Battle of Endor in 4 ABY, many of them were killed in the Stenax Massacres, when the Stenax invaded using stolen Imperial technology.