R2-D2 is the short, dome-topped "droid" (robot) in the popular Star Wars film series created by George Lucas. R2-D2 and his sidekick C-3P0 were a hit in the original film Star Wars (1977), where they served as comic relief as they aided heroes Princess Leia (Carrie Fisher) and Luke Skywalker (Mark Hamill). According to the storyline, R2-D2 is an "astromech droid" from the planet of Naboo, where he first served Queen Amidala (Natalie Portman). R2-D2 is operated by diminutive actor Kenny Baker.
Extra credit: According to Kenny Baker's official site, "R2-D2 was named when a technician from American Graffiti asked Lucas for reel number 2, dialogue track number 2."