C-3PO (phonetically spelled See-Threepio; 3PO or Threepio for short) is a humanoid robot character from the Star Wars universe who appears in the original Star Wars films, the prequel trilogy and the sequel trilogy. He was also a major character in the ABC television show Droids, and appears frequently in the Star Wars expanded universe series of novels, comic books, and video games. Along with R2-D2, he is one of only two characters to appear in all seven Star Wars films. C-3PO is played by Anthony Daniels in all seven films; C-3PO is one of two characters who are portrayed by the same actors in all seven films.

C-3PO is a protocol droid designed to serve human beings, and boasts that he is fluent in "over six million forms of communication". He is generally seen with his long-time counterpart, R2-D2. Threepio's main function is to assist etiquette, customs, and translation, so that meetings of different cultures run smoothly. While many protocol/interpreter droids range in color, C-3PO's own identifying colors are primarily gold finish, with silver from the right knee down.

Source: Wikipedia.