"My name's Dock. Mind if I ask who you are?" "I'm not Dock, I'm Xu. Dock's my brother." "All right, I'm Bushi! Let's get some river cleaning done."
— Dock, Xu, and Bushi each introducing themselves to Team Avatar.
Dock/Xu/Bushi was a Fire Nation citizen who suffered from dissociative identity disorder, splitting his personality between at least three different people. He lived in the small fishing village of Jang Hui, which was situated near a Fire Nation army factory. This facility spilled harmful toxins into the river on which the village was situated, out of which he drank, thus causing his mental dysfunction. Despite his disorder, the man seemed to be a reasonably productive member of his village and operated several businesses.
This villager's first personality, Dock, ferried people across the water and operated the docks, from which he stated he received his name. His second personality, Xu, whom he claimed to be his twin brother, operated the village's fish market. He claimed that he got the name Xu from operating the shop, though he did not understand why. He also introduced a third personality, whom he said was his brother Bushi. Each of his personalities were distinguished by the hat that they wore.
When Aang and his friends were preparing to clean the lake, they asked if Dock would like to help, to which he replied he would find his other brother Bushi, whom he said loved cleaning rivers. He then changed his hat right in front of Aang and his friends, though when Aang exclaimed to him that he had caught him, the villager became confused and said that he had no idea about what the Avatar was talking about. Finally, he seemed to catch on and said that his brother Dock was crazy and pretended to be other people, but this only further infuriated Aang.
According to Dock, Xu was a real blabbermouth, while his third personality, Bushi, claimed that his brother Dock was crazy.
Aang later wore the same hat Xu wore as the shopkeeper to hide his arrow in the Fire Nation.
In the end credits, the name for Dock/Xu/Bushi was just Dock. Likewise, his entry in Nick's old dedicated site also gave the character the name Dock, suggesting that Xu and Bushi are just other personalities he developed.
The name Bushi may be derived from the Chinese 不適, which means "unwell". This is a fitting reference to him being mentally unwell and might be used to show the irony when he calls his brother mentally unstable.