The well known protocol droid, C-3PO
Protocol Droids are a droid type primarily used for diplomatic purposes. These droids often speak a multitude of languages and are fluent in numerous forms of communication making them ideal for this purpose. A droid of this design often has a humanoid form as opposed to astromech or combat droids which often do not. The primary duties of protocol droids are be intermediaries and greeters and for this reason they are
unnarmed however it is not unheard of for them to used as portable traps or explosives in cases where one might wish to catch an enemy off guard. Protocol droids are very commonly used and probably used the second most of all work droids (astromech droids being the most common).