A three-legged R2 series astromech utility droid, R2-D2 usually teams with a fussy golden protocol droid named 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. 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.