R2-D2 is the Egg. His ability is to electrify pigs with a beam similiar to R2-D2's lightning beam seen in Star Wars Episode III: Revenge of the Sith. When getting up to the 8th Bonus level, R2 will receive an upgrade which makes is zapper more effective.
According to the Angry Birds Star Wars Character Encyclopedia, his official name is R2-EGG2. He is a devoted droid servant to the Jedi Birds and can act shell shocked sometimes, but others know that he will never let them down. he can talk to computers in a special language that others cannot understand. He looks harmless but hides The Egg, which contains the force. Both the Jedi and Sith are looking for it, and Yoda hid it inside R2-EGG2 to keep it safe. R2-EGG2 can record messages, which is used by Princess Stella to send a distress call to Obi-Wan.