Who is Keie from Parzival and what is their importance?

Keie is King Arthur's Seneschal. When Parzival first visits King Arthur's court, Keie mocks him and instigates his battle with Ither. He also hits Lady Cunneware for laughing when she sees Parzival because this means Parzival is destined to win, and eventually, Parzival avenges Lady Cunneware by unhorsing Keie in a joust.