Counterpart

"I am C-3PO, human-cyborg relations. And this is my counterpart, R2-D2."

- C-3PO introduces himself and R2-D2 to Luke Skywalker

A counterpart was one of a group of two or more droids who had worked together for a long period of time. C-3PO and R2-D2 were a famous pair of droid counterparts.

Appearances

 * Star Wars: Episode IV A New Hope