Rakkinishu

A large grey Rakk that swoops down and breathes fire on it's foes. It attacks the player while they are looking for Hidden Journals in the "Hidden Journal: Rust Commons West" quest. Drops loot just like any other boss/badass monster, but one item in particular is the Cracked Sash, a shield with a high recharge rate.

Rakkinishu is most likely a reference to a monster in the game Diablo 2, called Rakinishu. Also, the Cracked Sash shield is a reference to a Diablo 2 item with the same name.

Since Rakkinishu swoops down to close proximity to breathe fire, it's best to use a Shotgun.