C-3PO was known throughout the galaxy as the golden droid who worked with the Rebels.  But what was unknown to pretty much every one is that he started out as a cover-less robotic servant.  He was created on Tatooine by the human who would later be known as Darth Vader.  He was created to help Shmi Skywalker around the house but then was enlisted by Anakin to help R2-D2 clean and advirtise his podracer.  his master then left the planet to become a jedi.  He was reunited with his creator and R2-D2 on the trip to Geonosis.  He and R2 went through too many adventures to discuss here.  Eventually he and his counter part came into the service of the royal house of Alderann.  After being captured by Impearials they snuck into an escape pod and came into the services of Luke Skywalker, Coincedentally the son of his creator, but either due to being in service to so many masters or having his memory erased, he didn't recognize the name of Skywalker.  As Sky walker became more and more of a rebel hero so did Threepio.  After the dawn of the New Rebublic he served as a translator that helped win the NR many epic battles.  But his translating skills probably won't help the New Republic with the Yuuzhan Vong.