R2-D2 is an astromech droid. Astromechs are designed for starship management and repair. While they can understand most forms of speech, they speak in an electronic language of chirps, whistles, and squeaks which can be understood only by computers or other droids.
R2 is a brash droid. Bold, loyal, and a touch sarcastic. He is constantly bickering with his counterpart, C-3PO. He carried the Death Star plans to the rebels, saved Luke, Han, and Leia's lives several times, and was even aboard Luke's X-Wing when he destroyed the Death Star. This little droid is constantly at the center of events in the galaxy.