Clone Master

The Clone Masters were a group of renegade cloners who attempted an uprising against the Galactic Empire shortly after its founding.

Behind the scenes
Timothy Zahn, in his Thrawn trilogy, cast the Clone Masters as the opponent of the Old Republic in the Clone Wars, as he had been led to believe the cloners and their clones were the "villains." However, after Attack of the Clones revealed the clones were on the Republic's side, the Clone Masters were retconned into being renegades who did not attack until after the formation of the Empire.