I don't think you realize that our daughter has married a monster!
~ King Harold to Queen Lillian
King Harold (simply known as Harold) is the late husband of Queen Lillian, the late father of Princess Fiona, the late father-in-law of Shrek, and the former servant of the Fairy Godmother and Prince Charming. He is a major character of the Shrek franchise. He is an anti-hero-turned-major character in Shrek 2, a minor character in Shrek the Third, and a posthumous protagonist in Shrek Forever After.
King Harold makes his debut in Shrek 2. When his daughter Fiona arrives at the castle with her new husband, he is unpleasantly surprised that they are both ogres. King Harold had secretly made a promise to the Fairy Godmother that her son Prince Charming would marry Fiona. King Harold hires Puss in Boots to assassinate Shrek. King Harold then succumbs to guilt when Fiona finds out that Shrek is not around.
Harold at first refuses when the Fairy Godmother asks him to give the love potion to Fiona that will cause her to fall in love with Prince Charming, because he recoils from this invasion of her free will, but he is forced to acquiesce by some dark threat of disclosure; in the event, when Fiona states that she loved the old Shrek (rather the 'new' one that Prince Charming is pretending to be), Harold swaps the cup which contains the potion for his own.
At the ball toward the end of the film, Shrek is about to defeat Harold and the Fairy Godmother with help from his friends in order to save Fiona. However, Harold redeems himself and protects Shrek from a blast of magic from the Fairy Godmother's wand she used in order to get revenge on him for taking Fiona away from Charming, his armor causes the blast to reflect and kill the Fairy Godmother.
Afterwards, the king emerges from his suit of armor, now reverted to his original frog prince form by the blast. The wife seems not at all unhappy about this turn of events. After this, he apologizes to Shrek and accepts him into the family, his wife saying that he is more of a man for accepting Shrek and Fiona's marriage than he ever was when he was actually human.
Shrek the Third
King Harold makes a minor appearance in the third film in his water lily bed. Shrek does not want his father-in-law's crown; aside from not willing to give up his beloved swamp, he also doesn't think he's qualified enough to be a king. With his dying breath, Harold gives Shrek the name of the other possible heir: Fiona's cousin Artie. He then passes away, his body is placed in a shoebox, and pushed into a pond statue with everyone attending his funeral.
Shrek Forever After
Harold and Lillian make a flashback cameo trying to wager a deal with Rumplestilskin (who wanted Harold's crown so he could so he could rule Far Far Away). At the last instant, the king and queen are informed that Shrek had saved Fiona from the keep; rendering Rumpel's deal pointless.
Harold's death, as he passes away from his illness.
Although he is thought to the main antagonist in the second movie, The Fairy Godmother is the true villain of the movie, since Harold only wanted what he thought was best for Fiona while Fairy Godmother was just power hungry.
Harold has an Unexplained Recovery after the Fairy Godmother persumedly killed him as punishment for his Heel–Face Turn while saving Shrek at the final battle, but turned him into a frog in order to betray him.
Jeremy Irons, Tim Curry, Ian McKellen, Rowan Atkinson, Billy Connolly, Brian Blessed, Robin Williams, Robert De Niro, Paul Newman, Tony Jay, Jeff Bridges, Mel Brooks, Jack Palance, Simon Templeman, Jonathan Pryce, James Woods, Brian Dennehy, and Christopher Lloyd were all considered for the role of King Harold.
When King Harold was berated by the Fairy Godmother for not giving her the potion (since Fiona headbutted Charming), he explains without the slightest sign of fear that he gave her the wrong tea, with an obvious grin on his face. This indicated that he did that on purpose and this act hinted his next one when he shields Shrek from Fairy Godmother's magic.