He is the last of the distinguished family line of guardians of the Holy Grail. But he was  wounded. He was not only unable to fulfill his duties, he was also unable to father a next generation to carry on after his death. His impotence affected the fertility of his land, reducing it to a barren wasteland. All he could do was fish in the river near his castle and wait for the elusive “chosen one” who could heal him.

This episode is also available as a blog post: http://martinifisher.com/2021/03/08/the-fisher-king-and-the-divine-ancient-fishermen/