Abbot Mortimer was the mouse successor to Abbot Cedric and the predecessor to Abbot Mordalfus at Redwall Abbey. Old friends with Mr. Squirrel and Jess, he was also a close friend of Matthias and described as gentle and an extreme pacifist.
During the Summer of the Late Rose, he ordered the Redwallers not to attack Cluny's army when they were retreating. He was imprisoned when Cluny the Scourge captured Redwall Abbey. After Cluny threatened some of the Abbey beasts, Mortimer verbally defended them, which caused Cluny to assault the mouse with the poisoned barb on his tail. Mortimer died shortly thereafter. Before his death, he told Matthias not to become a brother of the Abbey, as it needed a Warrior. He also told Brother Alf to succeed him as Abbot.
He is so far the only Abbot or Abbess on record to die a violent death.