The Wounded King

Arthurian legend tells of a king who is charged with keeping the Holy Grail. This king is the Fisher King or the Wounded King. He is almost always wounded in the groin, but other versions say that he is wounded in his legs or feet. This wound never quite heals making it hard for him to move on his own and the wound has made him infertile. His injury affects not only himself, but his lands as well - the Fisher King's kingdom is a wasteland where the crops wither and all the king has left to do is fish from the river near his castle.

Ahab is very much the Fisher King within Moby-Dick. In Chapter 106: Ahab's Leg we as readers find out that Ahab's false leg had nearly pierced his groin before their journey began and left him in an incurable wound, much like the Fisher King. While one doesn't necessarily think about Ahab's wound, it becomes clear that this is another sign of foreshadowing with in the novel. Because of Ahab's wound the Pequod and its crew are headed for destruction, much like the Fisher King's wound and infertility led to the destruction and infertility of his kingdom. 

Moby-Dick is Ahab's Holy Grail. Ahab is searching for the white whale, but at the same time the whale is kind of in his charge. Ahab seems to know that no other whaling vessel will be able to defeat the whale, but in the back of his mind he must also know that he cannot defeat it as well. He uses his influence over his crew to keep going after Moby-Dick and he refuses to listen to reason. In the Fisher King story, knights from Arthur's court come to try and heal the Fisher King, but none are able to do so until Percival. In much the same way, Ahab is unable to reach Moby-Dick until Ishmael is on board. Ishmael doesn't cure Ahab, in fact Ahab becomes more insane as the story progresses, but Ishmael is able to write down the happenings and Ahab is finally able to face the beast who took his leg originally.

Both Ahab and the Fisher King rule over a particular space; Ahab over his crew and the ship, and the Fisher King over his land and people. They are both charged with keeping track of something valuable. Ahab keeps track of Moby-Dick and the Fisher King keeps track of the Holy Grail. They both think that the things that they are keepers of will give them piece of mind, but in reality Ahab only finds death while the Fisher King still sits on a throne that rules over a wasteland. In Ahab's case the whale is his undoing.