The Fisher King is another great symbolic film directed by Terry Gilliam, the other I love being The Imaginarium of Doctor Parnassus, which shares some elements with The Fisher King. "The Fisher King" is a reference to an Arthurian story, which has numerous versions. Essentially, the king is a seeker of truth or enlightenment (the Holy Grail stands for that) who has a wound that will not heal- until he does this and that. The same sort of healing trajectory is found in transformational/alchemical "fairy tales". Using my Jungian symbolic perspective, the character Parry is an inner figure of Jack's, some aspect of his psyche who was traumatized once, likely in childhood. The Red Knight is the pain, the suffering, the anger, and the fear that was born of the trauma.