In the movie he starts up hiding his true self and pretending to like Elsa and Anna, while he really wants to chase Elsa away by unlocking her and her kingdom's secrets, control the place and transport the riches to his country. He later offers Elsa a dance in order to take the crown, but Elsa states that her sister does, making him dance with Anna. Without Anna feeling, he asks her if she knows the reason why Elsa closed these gates up to now, and that shows he knows Elsa is hiding something you can take advantage of. Anna replies she doesn't know and stops dancing with him, but the greedy duke, wanting to brainwash Anna into talking more about it, says that if she wants another dance she will get one.
The Duke's Plan Success
Later, Elsa gets angry at Anna, she soon shows her snow powers, and the duke smiles and whispers to his guards that he knew there was something dubious he could take advantage of. Elsa then runs to the outdoors of the ca
stle, but the duke then frightens Elsa by ordering the thugs to stop her. The plan goes even better when she by mistake almost freezes the duke. The duke then says once monster softly while not looking shocked, revealing it is still part of the plan, and then shouts loudly monster in order to chase her away and celebrate victory on his plan. Later, he watches Anna and Hans running after Elsa, while looking quite happy about what is happening. When Anna comes past him he asks her if she has sorcery in her too in order to chase her away. Anna replies that there is no danger in herself or in Elsa and then Hans, contacting the duke at first, says Anna is completely ordinary, caring about her, and to not hurt her feelings says in the best way. The duke says she nearly killed him, in order to make Anna feel guilty and go looking for her. When Anna tells Hans she will go looking for her, the duke quietly whispers to his guard "yes!" meaning the plan is working also on Anna. Hans suggests to Anna to take him with but Anna puts him in charge of Arendelle, the city he wants to protect, and the duke gets angry for wanting to control Arendelle himself. He then looks at Anna leaving on her horse, not looking scared, expecting her to get killed as well on the way.
The Duke Recalculates Plans
After the duke starts thinking that Anna and Elsa are dead, the duke has time to get Hans against the citizens. He tells Hans not to waste his tradable goods, while not caring about the citizens. However, Hans angrily says Anna has given him orders to protect Arendelle. The duke tries to brainwash Hans into believing that Elsa is a monster and that Anna has teamed up with her. However, Hans doesn't believe it and says that he will not even think about handing Arendelle to a traitor.
After that, Anna's horse comes back, making the duke shocked about them being still alive. Hans starts realizing Anna is still alive but in trouble, and that makes him want volunteers. The duke sends his thugs to volunteer with the order to kill Elsa. When prince Hans goes with all his guards and the two thugs to Elsa's castle in order to ask Elsa if she has seen Anna, the duke’s thugs who came with try to complete the duke's mission. Hans tells the thugs not to kill Elsa, but they don't listen and hunt her anyway. Hans, while fighting Marshmallow, sees the two thugs running into Elsa's castle in order to try and kill her. Hans then comes in after a big fight and sees Elsa is guilty, telling her not to be the monster the citizens fear she is. When the duke's thug, stuck between ice walls, tries to shoot Elsa with a bow and arrow, Hans tries to shoot it up and miss her. But the arrow hits the crystal lamp at the top of the castle, and the lamp falls onto Elsa. Hans later from fear arrests Elsa while she's fainted, and tries to reason with her. When Elsa says she can't stop winter, the duke plotted with Hans.
When Anna came back, the duke looked at Hans in the eyes. It was revealed as the signal for Hans taking an act once he replied to the duke that something in the plan is wrong. While Hans revealed his new true nature towards Anna, the duke prepared the dignitaries for the plan, making them believe the fake conversation about Anna's death. They are convinced that Elsa should be punished, and because of the duke, royal guards went to kill Elsa. He then watches Hans trying to kill Elsa, making sure his plans haven’t failed. But Anna saves Elsa and the duke gets unhappy and is later discovered as a crimminal as he goes back to the jail in his own country, Weselton. After he was put into jail, no money or tradable goods are sent to Weselton by decree of Arendelle.
Evil, cold, wicked, cruel, ambitious and monstrous, as all he cared about is money and power, and as he would do anything to achieve his goals. Seeing the opportunity to kill Elsa, he took advantage of her powers, actually scaring the public and intending to control them. Near the end it was revealed that his panic was only to get Elsa into trouble, as he found excuses to stay away from jail, and he was anyway arrested for his crimes. He was at one point proven to show some tragic emotions, when he actually pretended to cry about Anna's death. However, he did so only to prove Elsa was a monster. Sending his two guards to help Hans find Elsa and secretly kill her, he had no emotions or excuses, as that was a very bright part of his true nature.