C-3P0 is played by Anthony Daniels;

R2D2 by Kenny Baker I

C-3PO is a protocol droid whose primary functions are etiquette and translation, making interaction between the myriad races of the galaxy possible. Protocol droids such as Threepio are particularly useful to diplomats like Princess Leia, who must be especially aware of the subtleties of custom and language among the other cultures they encounter. Capable of conversing in six million forms of communication, Threepio is particularly versatile, owing in part to his wide variety of experiences. These experiences have also given him a distinct, pragmatic and pessimistic personality, making him almost human in his perceptions and feelings. Often paired with his spirited maintenance droid counterpart R2-D2, Threepio serves as Artoo's interpreter for human masters.

A three-legged R2 series astromech utility droid, R2-D2 usually teams with C-3PO. Squat and barrel-shaped, Artoo-Detoo communicates electronically in a limited vocabulary of beeps and whistles, but his programming has evolved into a near-human personality that is both brash and bold.

Artoo-Detoo is designed to operate in deep space, interfacing with fighter craft and computer systems to augment the capabilities of ships and their pilots, usually from a socket behind the cockpit. Artoo monitors and diagnoses flight performance, maps and stores hyperspace data, and pinpoints technical errors.The meter-high droid has two treaded legs to provide mobility, and a third leg that can drop down for extra stability on rough terrain. Artoo also has floatation devices and a periscoping visual scanner which can guide the droid while he is submerged.

Artoo and Threepio have been at the heart of the Rebellion ever since their duty together on Princess Leia's consular ship, the Tantive IV. While serving as a diplomatic protocol droid aboard Tantive IV, C-3PO is unwillingly drawn into his counterpart's quest to find Obi-Wan Kenobi.

When the Princess' ship is overhauled and boarded by troops from the Imperial Star Destroyer Devastator, Leia programs R2-D2 with the vital stolen technical readouts of the Death Star. The little droid struggles to carry her secret message to Obi-Wan Kenobi, and comes to serve a new master, Luke Skywalker. As Skywalker's trusty companion, R2-D2 continues to play an important and ongoing role in helping the Rebels thwart Imperial forces.

Escaping the captured starship  in a life pod, Threepio and Artoo crash-land in the deserts of Tatooine to begin a new series of adventures. Wandering the dune sands alone, they are captured by Jawas and sold to their new master Luke Skywalker, setting him on a course of events that take him into high adventure amidst the Rebellion against the Empire.

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And here for the 6 million forms of communication of C3P0!
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