Hal the Boomerang Bird (sometimes referred to as Al, or Green Bird) is a character in the Angry Birds series of games created by Rovio Entertainment. He was introduced in 2010 and was the first new character added to the Angry Birds series who was not one of the original five birds in the flock, with the other three being Terence, Bubbles, and Stella in that order.
Al first appeared in Theme 6-4 as a prisoner, but was playable starting with Theme 6-5. He has appeared as a playable character in every version and episode of the game released since his introduction, though he is not necessarily in all levels. In the TV exclusive episode Sakura Ninja, Al appears dressed in kendo garb. This was the first time he has appeared in costume in any game and completely new game sprites were created for this.
The Angry Birds Wiki has more information about Hal