Examples of famous droids in film include R2-D2 and C-3PO of the Star Wars Universe, and less famous droids include: 2-1B medic, EV-9D9, the Trade Federation battle droid and super battle droid, Imperial probe droid, K-3PO, HK-47, R2-M5, R2-A6, R2-C4,HK-50, G0-T0, T3-M4, R4-P17, R4-D7, and the IG-88.
In the Star Wars universe, droids are used for many different purposes. Astromech droids (or Astrodroids) such as R2-D2 are used aboard starship for myriad purposes, including repair work and serving as central processing units or navcomputers for ships inherently lacking such, such as X-Wings. Protocol droids like C-3PO are used for diplomatic affairs and for translating. The two leading droid manufacturers are Cybot Galactica and Industrial Automaton.
The word droid originated as a contraction of "android"; in the novelization of Star Wars Episode IV: A New Hope the word was spelled with an apostrophe ( 'droid), a convention that has since been dropped. It is used to describe just about any robot, even those not humanoid in appearance. Some droids do, however, exhibit human-like behavior; for example, they may react emotionally or think intelligently and self-reflectively (best displayed in C-3PO).
It is widely believed that the hostility shown towards droids in Episodes IV-VI is a result of animosity as droids led the armies of the Confederacy of Independent Systems, the group widely (but erroneously) believed to be responsible for the Clone Wars. Expanded Universe authors have also attributed it to the Empire's general xenophobia and anti-alien bias; interestingly, even the Jedi (especially Obi-Wan Kenobi) seem to hold droids in low esteem, possibly because the droids have essentially no presence in the Force, but can be manipulated by way of the Force (see Irek Ismaren).