Until recently, my knowledge of Star Wars was based almost exclusively on countless viewings of the original trilogy, and a couple of viewings of the prequels. On this basis, I had assumed that the entire Imperial Army (i.e., the ground troops) was composed of stormtroopers. But I just read the canonical novel Lords of the Sith, and it makes a clear distinction between regular Imperial troops and stormtroopers:
“Bring more stormtroopers? They’ve got a bunch of conscripts and enlistees here now. Nubs looking for adventure, but not true soldiers. Maybe bring more troops, elite troops, and lock down Ryloth and spice production?”
- Star Wars: Lords of the Sith
And:
Fruun was one of Belkor’s men, one of the hundreds whose loyalty he’d bought through favors or secured through blackmail. Moff Mors - lazy, sloppy Delion Mors - left the running of Ryloth’s occupation to Belkor, and Belkor had not been idle. He’d filled several Imperial units with commanders whose first loyalty was not to Mors, or even to the Empire, but to him, and the soldiers would do exactly as their commanders told them. The stormtroopers were a problem, of course, but there weren’t very many members of the corps on Ryloth.
- Star Wars: Lords of the Sith
As far as I can tell, in the original trilogy we see the following:
- Stormtroopers: The rank-and-file ground troops, who come in several flavors (the most ubiquitous ones being the iconic image we all know as stormtroopers, plus the Snowtroopers on Hoth, and the scouts on speeder bikes on the moon of Endor), but all of them wear some variation of white plastic armor.
Generic Stormtroopers
Snowtroopers
Stormtrooper Scouts
Left to Right: AT-AT Driver, Stormtrooper Officer, Snowtrooper
- Army Officers: These guys usually wear dark grey/black cloth uniforms (except when they are filling special roles, like the AT-AT officer above, wh wears grey armor and a special helmet), but they order the stormtroopers around and say stuff like "You rebel scum!"
- Imperial Navy: The dudes on the Star Destroyers and Death Stars. Grey uniforms. They only appear to fight in space, not on the ground.
- Imperial Navy Pilots: The guys who fly TIEs. They wear black spacesuits and die even more quickly than their stormtrooper brethren.