Clone Force 99 was comprised of five CT-99 clones: Hunter, Wrecker, Tech, Echo, and Crosshair; each one possessed an enhanced skill set for service to the Galactic Republic.
CT-99s, clones with genetic defects, known by names such as Bad Batchers, 99s, defective CTs, or defective clone troopers (DCTs), were clone troopers whose genes were altered either through significant experimentation or as a consequence of the cloning procedure. Clone 99, who had physical limitations, was assigned to maintenance duty clone tasks, whereas Clone Force 99 members—Clone Sergeant Hunter, Wrecker, Tech, and Crosshair—had distinctive mutations that made them specialized soldiers within the Special Operations Brigade. Echo, though not originally born with differences like the others, seamlessly integrated into their group following his transformations as a CT-99 member. The Batch members each had a unique genetic mutation enhancing a particular skill, with the purpose of serving the Grand Army of the Republic throughout the Clone Wars. The genetic mutations affecting the Bad Batch also influenced their inhibitor chips, freeing them from the obligation to comply with Order 66. This order, issued by Supreme Chancellor Palpatine at the war's conclusion, commanded the Galactic Republic's clones to kill their Jedi leaders. However, Crosshair opted to obey the order and remain loyal to the Galactic Empire that succeeded the Galactic Republic.
One defective clone, Muzzle, functioned as an Advanced Recon Commando and later deserted the Republic. He secretly took command of the Aurodium Sword, a company of mercenaries, during the Clone Wars. The remaining members of Clone Force 99 defied the Empire by extracting the clone deserter Gregor from an Imperial base located on Daro. Initially, Gregor believed them to be clone commandos like himself until Hunter identified his squad as CT-99s, thereby revealing their status as genetically defective clones.