Clone Troopers were created in secret on Kamino, discovered by Obi-Wan Kenobi when he followed a clue to a murder. Clones, being genetically engineered for battle, with accelerated growth, were clones of Jango Fett, a well known and feared bounty hunter.
Clones served in the GAR, the Grand Army of the Republic, alongside the Jedi. When Darth Sidious commenced Order 66, the clones fired upon and killed the Jedi.
After the order, the clones became the first generation of Imperial Stormtroopers mainly as Trainers for the First Galactic Empire, however, some clones deserted the Republic and removed there Inhibitor chip.