R2D2 appeared in every Star Wars film (one of only 4 characters to do so), and is in most Star Wars media. He appears in almost every Star Wars game. In the original trilogy the R2 robot was a functional robot created by Petric Engineering and was also played by Kenny Baker, who would provide minimal movement animations such as making R2's head turn by pulling levers from inside the R2 unit. R2 was also radio controlled in many scenes. In episodes I, II, and III the original R2 unit was replaced by CGI versions of the character.
R2 has often been a "box of tricks" for the protagonists of the films, games and other media. Some of his gadgets include a gripping tool, a taser, a periscope, and a computer interface. In the original trilogy, R2 had a very strict set of "tools" at his disposal while in the prequel trilogy his gadgets were expanded to include jets, oil spray, and more.
The Original R2: sans special effects!