Although he's long claimed to be from the world of Fest, Cassian was once known as Kassa on Kenari. A lush jungle planet all-but destroyed by a mining accident, Kassa and his sister, Kerri, lived among a tribe of youngsters who survived on the untamed planet. When he was adopted by Maarva and Clem Andor at the age of 9, Cassian left Kenari behind, but could not shake thoughts of his sister.

On Ferrix, the young man grew up answering to the name Cassian Andor among his friends and neighbors. But Cassian understood the power of keeping a low profile. During a heist on Aldhani, he asked his fellow rebels to simply call him "Clem." Lying low in the aftermath of that mission, he adopted the alias "Keef Girgo" to avoid Imperial attention while vacationing on the resort world of Niamos. But Cassian couldn’t escape the Empire. In a twist of irony, he wasn’t arrested for any of his illicit rebel activities; instead, he was unlawfully detained on Niamos for loitering. Charged with “civil disruption,” Cassian, as Keef, was sentenced to six years of labor in an Imperial prison on Narkina 5.

Not long after he arrived, Cassian discovered all of the inmates were unknowingly serving life sentences without parole. He convinced his fellow prisoners, including Kino Loy and Ruescott Melshi, to band together, and together they staged a desperate breakout. Cassian returned to Ferrix to say a final farewell to his adoptive mother Maarva, who died while he was in prison. But the Imperial Security Bureau, which had identified him as a possible rebel, was expecting him. Resentment of the Empire’s presence spilled over during the funeral and the people of Ferrix rioted, giving Cassian the opportunity he needed to liberate his friend Bix Caleen and escape from the planet with Luthen Rael.

Cassian was more resolute than ever to contribute to the rebels’ cause. Over the next few years, he worked in Alliance Intelligence, where his duties included sabotage, reconnaissance, and assassination. Just before the Battle of Yavin, Captain Andor and his partner K-2SO recruited Jyn Erso to help the Rebellion find her father, an Imperial scientist. Through his efforts and the sacrifices of the entire crew of Rogue One on Scarif, the Rebellion retrieved the schematics of the Death Star and exploited its weakness in a decisive victory against the Empire.