Stormtroopers were elite shocktroopers who served in the Imperal Army. They were recruited humans. As opposed to Imperial Army troopers, they answered directly to the Emperor as they were marines that served the Imperial Navy. They were common sites across the Galaxy as many worlds supported the Empire. They were often armed with E-11 Blaster Rifles.
Stormtroopers were created after the transition of the Galactic Republic to the Galactic Empire in 19 BBY. The first stormtroopers were the existing Clone troopers of the former Grand Army of the Republic, specifically the 501st Legion.