Rillflag was Filorn's husband, father to Mhera and Deyna, and ancestor to Churk, Rumbol, and Skipper. His great-grandsire was also named Deyna. Shortly after his son's birth, Rillflag decided to perform an old otter ritual with Deyna, and took him to the ford to place him in water with a moving current.
After spotting watershrimp, Rillflag began to gather some to take back to Redwall Abbey. He was killed by Vallug Bowbeast on orders from Sawney Rath, who soon after kidnapped Deyna. Although Rillflag died, he continually appeared in both Deyna's and Mhera's dreams. Deyna was later said to be the very image of his dead father.