In Star Wars: A New Hope, the gold protocol droid who travels with R2-D2 is C-3PO.
C-3PO is a humanoid protocol droid fluent in more than six million forms of communication. He was created by Anakin Skywalker before the events of the original trilogy, although the first film presents him primarily as a nervous interpreter and reluctant companion.
C-3PO and R2-D2 are separated from Princess Leia's diplomatic mission when their ship is attacked by Darth Vader's forces. They escape to Tatooine, where they become involved with Luke Skywalker and Obi-Wan Kenobi. Their contrasting personalities—C-3PO's anxious speech and R2-D2's beeps—make them one of cinema's most recognizable robot pairings.
A common mix-up is reversing their designations: R2-D2 is the short blue-and-white astromech, while C-3PO is the tall gold protocol droid.