Duke of Weselton is a dignitary from Arendelle's neighboring kingdom Weselton, commonly mispronounced as Weasel Town (although if one is fluent in German language and pronunciation, it would be pronounced as VAY-zel-tun). His title proves he holds great power in his homeland, and on his formal wear, one will notice several badges and medals, indicating a history of significant accomplishment despite his rather meek character. He may also be the most powerful figure in Weselton aside from the ruler itself, though they're never mentioned or even alluded to. The Duke also has two burly bodyguards at his disposal, though they rarely speak and usually stand by the diminutive royal's side to protect from any and all harm. Even so, they do find their boss' character rather odd, considering their facial expressions during their introduction on Elsa's coronation day.
In relation to Arendelle, the Duke of Weselton controls the trading business between the two kingdoms, and notes that he's Arendelle's closest partner in trade. He's likely the closest visiting dignitary in the kingdom during Queen Elsa's coronation judging by his prominence throughout the events of the film. How long he's been associated with the kingdom and whether or not he knew the original king and queen before their deaths is unknown but highly likely.
Contrary to popular belief prior to the movie's release, the Duke of Weselton is in no way heartless or evil. He is, however, heavily pompous and greedy, though it's portrayed in a humorous manner throughout the film. Though invited to Arendelle for the coronation of Queen Elsa, the Duke was far more interested in exploiting Arendelle's tradable goods, as he's the representative of Weselton, Arendelle's former trade partner. He's also extremely interested in Arendelle's history, wanting to know why the castle gates were locked for so many years, and why castle grounds were off limits to outsiders, showing a nosy side of the dignitary.
The Duke's most striking trait is his cowardliness and irrational attitude. Whenever even the slightest oddity occurs, he'll go into a panic, relying on his bodyguard brutes to protect him. He also has a hatred of magic and "sorcery", reason being he finds it to be highly dangerous, explaining why he was so hostile towards Elsa after her powers were revealed at the coronation ball. His fear of magic and the mysterious power it holds is what leads him to perform his only immoral act, which was ordering his thugs to find and kill Elsa, hoping her death would result in the eternal winter curse she accidentally caused to be lifted.
However, despite his flaws, the Duke does have a heart to some degree. He's shown to care for the safety of others, besides himself, as seen when the dastardly Prince Hans claimed Princess Anna was killed by Elsa, the Duke finding the news to be immensely shocking, especially considering the princesses' family ties. This can also be seen again during the chase sequence at the coronation party, where the Duke held a distraught expression as Elsa ran into the crowds in the castle courtyard, likely showing concern for the vulnerable denizens.
Role in the film
Arriving in Arendelle
The Duke of Weselton is first seen with his bodyguards entering Arendelle and nearing the castle gates. The greedy royal proves to be extremely excited, deeming Arendelle his most mysterious trade partner, and that he greatly looks forward to unlocking its secrets and exploiting its riches. Along with the other dignitaries, the Duke attends Elsa's crowning coronation as well as the ball thrown in honor of her first night as queen. Anna and Elsa's majordomo, Kai, introduces the snooty duke, which is when the short royal offers Elsa her first dance as queen, claiming he should have the honor being their closest partner in trade. Elsa rejects the offer politely, but volunteers Anna, to which the Duke agrees to nonetheless. Though he believes otherwise, he's a terrible dancer, constantly stepping on Anna's toes and making a complete fool out of himself. The entire event was merely a chance to become closer to the two princesses, hoping a close relationship would further enhance his trading business with Arendelle. In the middle of his routine, he questions the princess as to why the castle gates were closed for so many years, to which she nervously claims ignorance.
Not too long after the comedic scene, Anna and Elsa get into an argument, and the drama causes Elsa's secret power over ice and snow to be revealed. The fearful Duke calls her out, claiming it to be dark magic, sorcery, and orders his men to capture her the moment she flees, though he and his goons were nearly killed by an accidental blast caused by the queen, resulting in the Duke calling her out as a monster. Anna, the visiting Prince Hans, and the Duke follow after the queen, who escapes into the mountains, accidentally casting a powerful curse over Arendelle, putting it into an eternal winter. It begins to snow eerily throughout the land, causing the citizens to worry, though the Duke immediately becomes irrational, panicking, albeit humorously. He then suspects Anna to have powers as well, but the princess denies and explains that Elsa means no harm. The stubborn Duke finds it hard to believe, as she nearly killed him with her magic during the chase. However, to free the land from the curse, Anna volunteers to go after the queen. The Duke immediately agrees, but her fiancé, Prince Hans wasn't too fond of the idea. Nevertheless, Anna departs and leaves Hans in charge.
Later on, back in Arendelle, things have become worse with the snow having become ice, freezing the entire kingdom, and the living conditions become unbearable for the citizens as, due to the curse overcoming the land in the middle of summer, no one is prepared for the harsh winter weather that's arrived. Hans and the royal guards are busy giving away free cloaks and other necessities for the kingdom's inhabitants who are struggling to survive, much to the Duke's dismay. The Duke scolds Hans on his actions, not wanting the prince giving away any of Arendelle's tradable goods instead of taking action against Elsa, believing Anna's merely conspiring with her to doom the land. However, the Duke is soon forced to silence himself when Hans snaps at him, threatening the Duke with his power to have him arrested for treason. Disgusting by Hans' claims, the Duke's silenced until Anna's horse returns alone. Hans feels the princess is in danger, and asks volunteers to journey to Queen Elsa's palace with him to find her. The Duke volunteers his bodyguards, and secretly orders them to eliminate Elsa should they find her so they could put an end to the winter.
Back in Arendelle
With Hans in charge, the bodyguards journey to Elsa's ice palace where they ignore Hans' orders to bring no harm to the queen and barge into the icy walls, immediately taking action. However, soon enough, Elsa gains the upper hands and uses her abilities to battle the duo, nearly killing them until Hans intervenes. Even so, the Snow Queen is captured and imprisoned, though the order given to the Duke's thugs either remained confidential or ignored, as the Duke wasn't seen given any punishment or word on the matter, though the thugs weren't seen again for quite some time, likely suspended as punishment for disobeying Hans' commands. Meanwhile, in the castle parlor, Hans decides he'll go back out in an attempt to find Anna, but one of the dignitaries suggests he stays behind, as he's all Arendelle has should Anna fail to return. Just then, however, she does, and desperately asks Hans to kiss her, prompting the Duke and the others to leave the room, giving them some privacy, completely unaware that the prince is actually villainous and power-hungry, planning to betray Anna to steal the throne. Moments later, Hans returns looking distraught just as the Duke declares action be taken once again. He tells them Anna was killed by Elsa, and that they said their marriage vows just before she died in his arms, thus making him king of Arendelle. The claims were lies, but the Duke and other dignitaries are oblivious to the fact, and Hans sentences Queen Elsa to death.
A Fitting Comeuppance
Moments later, Elsa accidentally causes a powerful blizzard to break through as she escapes her prison, and the Duke of Weselton joins the other dignitaries who rush onto the castle balcony to see what the chaos was. From there, they are able to witness Anna sacrifice herself to save Elsa from the treacherous Hans, and mourn for her death once she freezes solid doing so. Fortunately, she thaws soon enough, as well as the entire kingdom after love is revealed to be the breaker of Elsa's curse. The Duke and the dignitaries all rejoice once peace was restored. The Duke, however, is cut off from trading with Arendelle by orders of Queen Elsa, due to his earlier attempt to have her killed. The Duke tries to claim he was innocent and a victim of fear, but to no avail, and he and his thugs are sent back to Weselton, which he is heard insisting is not named "Weasel Town" after being mispronounced once again, though purposely by Kai to annoy him.
Role in the Spongebob Series
This character is offitcally scrapped out of the SAF series. Though he fact that this character's page isn't deleted by now is perhaps an indication that he may be subjected to a different role in mind.