Prince of Florin, he becomes betrothed to Buttercup (in the novel on the excuse that he will need to continue the royal line because his father is dying). He does not care who his bride is, as long as she is very beautiful. Count Rugen then finds Buttercup.
After pursuing Buttercup and her kidnappers, Buttercup has him swear not to hurt Westley, but instead he lies. Humperdinck tells Westley and Buttercup to surrender but they do not listen. It is revealed he hired Vizzini to kidnap and kill her, and now is planning to murder her on their wedding night and framing Guilder like before, and he will have a political reason for declaring war. Unfortunately his plans are thwarted by Westley, Inigo Montoya, and Fezzik, but they let him live instead of killing him, leaving him to pursue them when they escape with Buttercup.
The primary antagonist, Prince Humperdinck is incredibly intelligent, cocky and has excellent tracking and hunting instincts. He can track the location of animals, and is able to trace events that have happened in a particular place. Buttercup herself says there is no greater hunter than him, proclaiming that he "Can track a falcon on a cloudy day."
Humperdinck is the prince of the fictional kingdom of Florin. He is the finest hunter in the world; his tracking abilities are so great that he is able to tell which of two sets of tracks belonged to the loser of an hours old sword fight, and to determine that a wrestling match had occurred between a man and a giant. Behind his princely demeanor, however, he is vain and cowardly, "with a heart full of fear".
He plans to marry Buttercup, the story's heroine, ostensibly so he can inherit the throne from his senile father and father an heir. He has hidden plans, however; he hires the criminals Vizzini, Inigo Montoya, and Fezzik to kidnap and kill her, hoping to implicate the nation of Guilder in her death so he can start a war. Her true love Westley (title: the Dread Pirate Roberts) defeats his assassins and saves her. However, after tracking them through the Fire Swamp, Humperdinck reclaims Buttercup and throws Westley into the Zoo of Death (the "Pit of Despair" in the movie'), his secret dungeon, to be tortured by Count Rugen, his second-in-command. When Buttercup threatens suicide if she is not reunited with Westley, Humperdinck pretends to respect her wishes and send for his rival's return, confident that the other man will be dead long before the wedding.
When Humperdinck accidentally reveals that he didn't send for Westley, Buttercup loses her temper and calls him a coward. Enraged, he descends into the Pit/Zoo, where Rugen has Westley attached to a machine that drains years of life away, and turns it to "maximum", leaving him "mostly dead".
He forces Buttercup to marry him later that night, planning to strangle her and blame it on Guilder. He is thwarted by Westley, who returned to life with help from Fezzik, Inigo and Miracle Max, the king's former "Miracle Man" Miracle Max who had been fired by Humperdinck. Westley challenges him to a duel, even though Westley can barely stand due to the aftereffects of being resurrected. Humperdinck is unaware of Westley's condition and agrees to duel him "to the death!" But Westley warns him that it will be "to the pain" instead, and explains what this means: he will not kill Humperdinck but leave him hideously deformed. Terrified, Humperdinck surrenders, and is left tied to a chair in the honeymoon suite of his own castle as Westley escapes with his bride. In the book, his men save Humperdinck, and he pursues the 4 heroes (Westley, Buttercup, Fezzik and Inigo), leaving the book on a cliff-hanger.