Source : Webster's Revised Unabridged Dictionary (1913)

Bellower \Bel"low*er\, n.
   One who, or that which, bellows.

Source : WordNet®

bellower
     n : someone who communicates vocally in a very loud voice [syn:
         {roarer}, {bawler}, {screamer}, {screecher}, {shouter}, {yeller}]