In early 2009, Rovio staff began reviewing proposals for potential games. One such proposal came from senior game designer Jaakko Iisalo in the form of a simulated screenshot featuring some angry-looking birds with no visible legs or wings. While the picture gave no clue as to what type of game was being played, the staff liked the characters, and the team elected to design a game around them. As the concept of Angry Birds was developed, the staff realized the birds needed an enemy. At the time, the "swine flu" epidemic was in the news, so the staff made the birds' enemies pigs. Angry birds was the studio's 52nd game for the iPhone where it reached No. 1 spot in the Apple App Store chart after six months and then stayed there for months. The initial cost to develop Angry Birds was estimated to exceed €100,000, not including money spent on the subsequent updates. For the iOS version, Rovio partnered with distributor Chillingo to publish the game to the App Store. Chillingo claimed to have participated in final game polishing, such as adding visible trajectory lines, pinch to zoom, pigs' grunts, birds' somersaults on landing. Since then Rovio has self-published almost all of the later ports of the game, with the exception of the PlayStation Portable version, which was produced under license by Abstraction Games and then distributed by Chillingo.
Source: Wikipedia
