Cow King's Hide

Source
Despite not being within this item's normal level range, Ragnaros and Nefarian have a chance to drop it as well.

Trivia

 * Cow King's Hide is a reference to an item of the same name in Diablo II. The item could only be found in the Secret Cow Level, which contained Hell Bovines and the Cow King. For stats on the Cow King's Hide in Diablo II, see Cow King's Leathers.