King Harold is one of the two overarching protagonists (alongside Queen Lillian) of the Shrek franchise.
As revealed in the end of Shrek 2, he was The Frog Prince from the fairy tale of the same name (not to be confused with the Disney version). He does not appreciate the fact that his daughter, Princess Fiona is married to Shrek because she was supposed to marry the prince he choose for her. In the end, he redeemed his thoughts about Shrek and his daughter and during the final battle, he was turned back into a frog while defending Shrek from the wicked Fairy Godmother.
He was voiced by John Cleese.