C-3PO ([si ˈθɹi pi ʔɔw], nicknamed Threepio) is a fictional character from the Star Wars universe, who appears in both the original Star Wars films and the prequel trilogy. He is also a major character in the television show Star Wars: Droids, and appears frequently in the series' "Expanded Universe" of novels, comic books, and video games. C-3PO is one of the four characters to appear in all six of the Star Wars feature films, and the only one to be played six times by the same actor. In all his various appearances, he is portrayed by Anthony Daniels.

C-3PO is a protocol droid designed to serve humans, and boasts that he is fluent "in over six million forms of communication." C-3PO is generally seen with his long-time counterpart, R2-D2, a small, quirky astromech droid. Threepio's main function as a protocol droid is to assist with etiquette, customs, and translation so that meetings of different cultures run smoothly. In his time, C-3PO loyally served over forty masters. He hated adventure and space travel, as they often resulted in him coming out on the wrong end of a fight, losing parts, and having them reattached, sometimes incorrectly. Together with his fellow droid R2, Threepio played a vital and pivotal role in the Galaxy's history, however lowly he thought of himself.