A Boss is a type of enemy used in the Angry Birds series. Compared to a standard enemy, which is often immobile and can be downed with a single Bird, bosses on the other hand are very mobile, and can survive several direct impacts.
Bosses first appeared in Angry Birds Rio, with Nigel being the first boss in Angry Birds history. Angry Birds Space, Star Wars, and Star Wars II are the only other games in the series to contain a boss.
Bosses are not to be confused with major enemies, which while slightly more powerful than a standard enemy, do not meet the requirements to be a Boss.
In games that feature bosses, a boss will appear in the final stage of most themes. They are usually the only enemy present on-screen, though standard enemies may occupy the boss' level as well. In that case, both the boss and his/her minions must be defeated to win the level.
The available Birds to use are more varied, usually including one of next to every major character using the slingshot. The boss' level is usually arranged with many additional targets to strike besides the boss itself and any minions it may carry, which will launch blocks at the boss to deal additional damage. Once the boss is defeated, they will be knocked off or leave the stage, declaring victory to the player.