R2-D2, phonetically spelled Artoo-Detoo or Artoo, was an astromech droid and undoubtedly the most famous unit of the R2 series. A longtime friend and counterpart of the protocol droid C-3PO, he served the Skywalker family faithfully for many years. Along with his resourcefulness, R2-D2 was equipped by his original owners, the Royal House of Naboo and the Royal Naboo Starfighter Corps, with many tool-tipped appendages that allowed him to serve as a superior starship mechanic and computer interface specialist. A bold droid in personality and temperament, R2-D2 would often enter dangerous situations without second thought in order to give aid to his masters. This adventurous streak served his companions well on numerous occasions, often turning the tide of galactic history.
R2-D2 was a diminutive droid, standing 0.96 meters tall. He rolled on three legs, one could retract into his body, and had a silver and blue domed head. His white, blue, and silver body housed many arms, sensors, and other apparatuses, many of which were not readily seen by the typical humanoid eye. This often made the droid seem like a box of tricks, unexpectedly pulling out some previously unseen but much needed device at a critical moment.
While R2-D2 contained many specialized gadgets, he was also quite good at taking the initiative and often employed unorthodox means to help his friends.
In 2003, R2-D2 was in the inaugural class inducted into the Robot Hall of Fame. See: http://www.robothalloffame.org/inductees/03inductees/r2d2.html
The May 2014 issue of Smithsonian
magazine, pp. 68-69, has an article by Clive Thompson titled "Almost Human: How R2-D2 became the most beloved robot in the galaxy".