The Imperial Stormtroopers are the elite soldiers of the Galactic Empire. They are the main ground force of the Empire and are seen in all three of the original Star Wars trilogy.  They are instantly and iconically identifiable by their famous white and armour.

There are also specialised units that be seen in some of the films.  Notably the Sandtroopers in Star Wars Episode IV: A New Hope and the Snowtroopers in Star Wars Episode V: The Empire Strikes Back.

This simple but effective illustration is how I imagine a recruitment poster might look.