Tso was a male Human Major of the Galactic Republic's Viridian Squad living during the Galactic War. Following the Battle of Rishi, he was part of Satele Shan's force that traveled to Yavin 4 and established the anti-Revanite coalition along with Imperial forces under Darth Marr. During an excursion into the Massassi territory, the squad was ambushed, with commanding officer Era Jung dead and the rest taken captive. After a fellow Coalition member rescued the prisoner, he informed Major Tso of Sergeant Jung's death.