The prisoners were captured by the Galactic Patrol during the many years it was active, with the likes of Moro being captured ten million years ago, while Cranberry was imprisoned sometime after the Battle of Namek.
Main article: Galactic Patrol Prisoner Saga Regaining some of his magic power, Moro escaped the Galactic Prison alongside Cranberry. During their attack on Namek, Moro kills Cranberry and uses the last wish on the Namekian Dragon Balls to free the prisoners from Galactic Prison to act as his army.
The power of each prisoner varies. When Moro shared some of his energy with the prisoners, during the prisoner's group attack on Goku and Vegeta in their Perfected Super Saiyan Blue forms and Good Buu as the Grand Supreme Kai they were no match, with each being downed in a single hit. However they were capable of taking on Goku and Vegeta's base forms. When Moro stole energy from Goku and Vegeta, a pair of prisoners grew strong enough to fight Goku and Vegeta in their Super Saiyan forms.