King Bull Sparra was the clever and mentally unstable monarch leader of the Sparra tribe who lived above Redwall Abbey. He was the brother of Dunwing and uncle of Warbeak. Having no fledglings of his own, he maintained a soft spot for Warbeak, regarding her as his favorite niece. King Bull inherited the sword of Martin the Warrior from his predecessor, King Bloodfeather.
While hunting for worms in Mossflower Woods with his brother-in-law, King Bull Sparra was attacked by Asmodeus Poisonteeth and dropped the sword during the melee. Asmodeus then took possession of the sword, and King Bull Sparra ordered Greytail to retrieve the symbolic weapon. Greytail attempted to get the sword back, but he was bitten by the adder. Miraculously, he did not die instantly, and upon returning to the Sparra court, Greytail told Dunwing what really happened while King Bull Sparra told the others that Greytail's injuries were caused by a starling fight. King Bull pretended that he still owned the sword to maintain his role as leader, and Greytail died of his wounds shortly after.
King Bull Sparra captured Matthias when he climbed up to the Sparra court. Due to the pleas of his sister and his niece, he spared Matthias' life, but enslaved him for her. He had a special fondness for candied chestnuts, which he repeatedly demanded from Matthias.
King Bull Sparra observed that Matthias' belt was derived from the same leather as his scabbard and took it from him. On the day that Matthias escaped the loft, King Bull Sparra was led to believe that Asmodeus was spotted in Mossflower dying with Martin's sword due to a rumor started by Dunwing. After hiding the scabbard and belt underneath an old armchair in his quarters, King Bull Sparra led a party of warriors to locate the adder.
Unsuccessful in his search, he flew back to Redwall. Noticing Matthias on the roof waving the scabbard and belt for Jess Squirrel, the sparrow attacked Matthias and dug his claws into the belt, however he was knocked senseless by the mouse's scabbard. He fell off the roof and dragged Matthias down with him.
His lifeless body was found by Brother Alf and Constance with the injured Matthias in the Abbey pond. A portion of his beak was lodged in Matthias' shoulder.