Sixtus Quin was an operative of Imperial Special Intelligence. He would later betray the Empire and join the Alliance to Restore the Republic. After his time with the Rebellion, he partnered with Elscol Loro to establish an anti-Imperial mercenary organization.
After Captain Marl Semtin betrayed Quin and his elite team, they deserted the Empire. At Eidolon Base on Tatooine, Sixtus eliminated Semtin. Subsequently, his squad allied with Elscol Loro, a former pilot of Rogue Squadron, to create an anti-Imperial mercenary group.
In 7 ABY, after they departed the New Republic to fight the Bacta War against Ysanne Isard, members of Rogue Squadron recruited Sixtus and Elscol. To establish a native Vratix insurgency and overcome Isard's forces on Thyferra, Sixtus, Elscol, Mirax Terrik, Iella Wessiri, and Corran Horn were deployed to the planet. Despite a clash at the spaceport and assaults on the Vratix by Isard's soldiers, Sixtus successfully formed a strong resistance. Sixtus participated in a strike team that executed a raid on the Dlarit estate to embarrass [Aerin Dlarit](/article/aerin_dlarit], the father of Erisi Dlarit. As the Rogues and their comrades battled Isard's flagship, the Lusankya, above Thyferra, Sixtus and the insurgents stormed Isard's headquarters. They successfully captured Fliry Vorru, although Isard managed to escape aboard a shuttle. The Bacta War ended in triumph, and Isard was believed to have perished.
Michael A. Stackpole had not initially envisioned Sixtus as black; John Nadeau, the illustrator for Star Wars: X-Wing Rogue Squadron: Battleground: Tatooine, made that decision.
Although his exact military rank is not specified, Sixtus's rank badge suggests he could have held the rank of either Lieutenant or Captain while serving in the Imperial military.