This Character Bio was written by me.
Seiyuu: Ikue Ohtani
Position: Doctor
When Chopper was a young reindeer living in his herd in the snowy wilderness of Drum Village, he was shunned and ignored because of his unusual blue nose. After he accidentally ate the Human Human Fruit, his situation grew worse. The Fruit gave him the ability to transform not just into a reindeer form, but also a human form, and an in-between form. He also gained the ability to think and speak like a human. This made the herd despise him even more and he was finally kicked out. One night, lonely and depressed, Chopper wandered towards Drum Village. But even though he was in his human form, his fur and blue nose were still intact and the villagers thought he was the rumored abominable snowman. Terrified, they gathered their weapons and brutally attacked him. But luckily he was rescued by Hiluluk, the village's "quack" doctor, who found him and nursed him back to health. During the year they spent together, Hiluluk became the first human that Chopper grew to trust. They had a lot of fun together and Chopper finally began to feel accepted. Hiluluk gave him the name of "Tony Tony Chopper" and he even called Chopper his son. He told Chopper not to hate humans; the village at the time was in a state of turmoil because of its wicked king Warpol. He also told Chopper about the dream he had been working towards for 30 years; constructing a potion that would make sakura (cherry blossoms) bloom in Drum Village, which was covered in snow all year round. Before he was a doctor, he was a thief, but after seeing sakura bloom, he changed for the better and became a doctor...he believed that sakura blossoms could even cure a "sick" village.
Promptly after Chopper was fully recovered from his injuries, Hiluluk unexpectedly kicked him out. Hiluluk knew that his health was declining and he was right...the next day he found out he was going to die in two weeks. Chopper overheard him telling this to Kureha, another doctor in the village(who was sometimes called a "witch" because of her eccentric personality.) Desperately, Chopper went out seeking a mushroom which he thought could cure Hiluluk. But the mushroom was actually poisonous. Despite this, seeing how badly hurt Chopper had become trying to get it for him(he had gotten into a fight with his old herd on the way) Hiluluk ate the mushroom(he was going to die soon anyway.) Meanwhile, Warpol was devising an extremely evil plan; he was going to exile or kill all the doctors in Drum Village and keep only 20 as his own private doctors in the castle. That way, if anyone wanted medical care, they would have to bow down to Warpol first. He then set a trap to lure Hiluluk to him; he announced that all 20 of his doctors had become sick and were unable to treat anyone. So Hiluluk rushed to the castle to try and cure Warpol's doctors, despite the fact that he himself was close to death. After Chopper found this out, and that the mushroom he had given Hiluluk was poisonous, he rushed to the castle, but it was too late. Once Hiluluk had found out Warpol's plan, he chose to die by drinking some of his own lethal poison, rather than die by Warpol's army or Chopper's mushroom. Afterward, Warpol and his men were driven out of Drum Village, although the only doctor left was Kureha. Chopper begged her to teach him how to become a doctor too. She finally agreed and the two took residence in Warpol's old castle.
Chopper first met Luffy and his crew many years later, after he had already gained a lot of medical knowledge from Kureha and acted as her assistant. Luffy and the crew had stopped at Drum Village because Nami had gotten very sick from a bug bite and they were desperately seeking a doctor. Kureha and Chopper found Luffy after he risked his life climbing to the peak of the high cliff where their castle was located while carrying both Nami and Sanji(who had gotten hurt in an avalanche.) After treating them and letting them stay at the castle to recover, Luffy was impressed by Chopper's medical skills and the fact that he was a "cool" transforming reindeer. He then decided that he wanted Chopper to join his crew. Chopper refused at first, but after Warpol and his men made an unexpected return and Luffy fought against and defeated them and even prevented them from destroying Hiluluk's flag, which flew at the top of the castle, Chopper began to have second thoughts. He finally made his decision to join them the same night that Kureha had the villagers shoot off Hiluluk's miracle sakura potion into the sky through cannons...and miraculously it was a success and the sky above Drum Village grew sakura pink and the blossoms fell like snow. With Hiluluk's wish finally realized, Chopper tearfully left Drum Village with Luffy's crew, despite the fact that Kureha didn't want to lose her assistant(or "son.")
Not only does Chopper know a variety of medicines and cures, but since he's a reindeer he can understand the languages of other animals, as well as people. He's much more shy and soft-spoken than the rest of the crew, perhaps from the loneliness of his past. But joining them has definitely opened up his heart and given him the friendship and fun that he had been so terribly deprived of.