El Pollo Grande<The Black Chicken of Death> is a huge black level 50 chicken summoned by Niby the Almighty in Felwood. It is classified as a beast and is not tameable. It has no loot.
Niby summons this ferocious fowl when you turn in the quest  Kroshius' Infernal Core. It was not his intention to summon a demonic chicken, but rather something that he could use to extract his revenge on Stormwind City.