Jet and the other Freedom Fighters came across The Duke when they caught him trying to steal food from their camp. According to Jet, The Duke never really had a home, indicating he was probably orphaned at a very young age by the Fire Nation.
Being a constant companion to Pipsqueak, the duo originally appeared as guerrilla fighters, assisting Jet in the fight against the Fire Nation occupation of Gaipan. When Aang, Katara, and Sokka were cornered by a company of Fire Nation soldiers, The Duke and the other Freedom Fighters came to the rescue. During the ensuing battle, The Duke dropped out of a tree, right on the helmet of one of the soldiers and rode him "like a wild hog monkey". When Jet introduced his Freedom Fighters to Team Avatar after the battle, Aang mistook The Duke for being Pipsqueak. After snooping through the camp's supplies, The Duke and Pipsqueak found barrels full of blasting jelly and boxes filled with jelly candy. The Freedom Fighters loaded up the loot in a cart and headed back to their hideout, where they would have a feast to celebrate their victory over the Fire Nation soldiers.
A few days later, The Duke was among the Freedom Fighters who headed out at night with a cart filled with barrels of blasting jelly. When Jet was explaining his plan to blow up the dam with the jelly and subsequently flood Gaipan and everyone living there, The Duke voiced concern for the people, something Jet countered by stating that it was "the price of ridding this area of the Fire Nation". The Duke then moved on to help Sneers and some other Freedom Fighters to place the barrels full of explosives at the base of the dam.
After Aang, Katara, and Sokka stopped Jet's plan to destroy the village with a flood, Pipsqueak and The Duke lost faith in their once idolized leader and parted ways with the Freedom Fighters. They then traveled through the Earth Kingdom, stealing to eat and struggling to survive. The two eventually came across Hakoda's ship one night and attempted to raid it, but were caught in the act and captured. After hearing their story, Sokka and Katara welcomed Pipsqueak and The Duke to join their makeshift invasion force. During their time at Chameleon Bay, they were described as "surprisingly helpful" when they were not getting into trouble.
The Duke and Pipsqueak returned with Hakoda and the others the day of the Day of Black Sun, ready to do their part in the Invasion of the Fire Nation. The Duke easily got along with Toph, even offering her his helmet when she got seasick traveling in a waterbending-powered submarine. However, the invasion failed, and with the destruction of the submarines, the warriors decided to surrender. The Duke parted with Pipsqueak when the young boy was among those who made their escape atop Appa, along with Aang, Katara, Sokka, Teo, and Haru.
The Duke was temporarily part of Team Avatar when they occupied the Western Air Temple after their defeat during the invasion. There, The Duke, Haru, and Teo explored the temple's many secrets together, during which the other two often referred to him incorrectly as just "Duke". When Fire Nation airships attacked the Western Air Temple under PrincessAzula's command, the gang was forced to abandon the site. The Duke, Teo, Haru, Hakoda, and Chit Sang separated from Aang's group, and fled the temple on a previously stolen airship.
After the Hundred Year War ended, The Duke returned to the Fire Nation for Zuko's coronation as the new Fire Lord. There, he reunited with Pipsqueak, and hugged Toph.
The Duke was very sensitive of people calling him by his full name, namely "The Duke". He corrected many people, including Haru, when they called him "Duke" instead of "The Duke". However, when Jet called him "Duke", he did not say a word.