Tony Tony Chopper is a pirate doctor from the Straw Hat Pirates group. He was originally a deer that could transform into humans after accidentally eating the "Hito Hito no Mi" Devil Fruit. By the World Government, he was misinterpreted as a pet straw hat crew and was only blessed with a bounty value of  50 after the event at Enies Lobby. His dream with a straw hat crew which is to cure all diseases in the world including being able to see the vastness of the world according to Dr. Hiluluk.
Appearance
In most of the time, Chopper is a small human deer half deer. In this form, he walked on two legs, but the whole body part came from the shape of a deer, such as; has fur, the shape of the nose, hands and feet and has horns. Chopper's left horn was tied with a metal plate because it had been damaged when searching for Amiudake mushrooms when he was young. He wears a red hat with a white cross (a red cross that is sideways) that is rarely opened and a pair of red shorts. He also sometimes carries a blue backpack on his back with the same white cross. He has a cute blue nose that is his trademark. His blue nose is the only thing he can't change when transforming in any form.
In the form of a deer, the horn becomes more branched and long, but overall its appearance is like a normal deer. In human form, it looks like a human but has fur all over the body, and its arms and legs look longer. In the form of a Gorilla, he looks like a human, but gets taller and his muscles become more muscular. In the form of a monster, it changes to be very large like a giant and has a longer head feather like hair. In addition, the shape of the muzzle of his head is like a deer even though it still runs on two legs.
Like the habits of other male crew members, Chopper's dress style is almost the same in every series. When in Alabasta, he wore a white shirt with green stripes covered in an open purple shirt with purple stripes. After the war ended, he wore a yellow shirt that was visible for him to cover his ankles. While at Enies Lobby, he wore a red leather jacket.
After the timeskip, Chopper wears a new blue hat decorated with small white circles around a larger circle. This larger circle has white stripes with a red base and there is a sideways white cross symbol. He also wore white yellow vertical stripes and orange shorts. He can also transform into a new form; Kungfu Point. In the form of Kungfu Point, his appearance was similar to the shape of Brain Point, but his face changed oddly in terms.
In addition, in the form of the original deer, he grew tall with almost the same as Usopp. The horn also grows bigger and has more thick muscles and feathers. In the form of Heavy Point, it becomes very large and more muscular. In the form of Chopper Guard Point covered in fur that is very thick, like when protecting the Thousand Sunny. Whereas in the form of a Horn Point, the horns become longer.
Characteristics
Chopper is shown to be very shy, innocent, naive and spoiled like a child. Similar to Luffy, he is easily impressed with dazzling things like cannons, robots or other things. He can also be a coward like Nami and Usopp, even though it is more associated with his childish nature. During an adventure with a straw hat crew, Chopper tends to follow the behavior of other crew as a model or in other words he is more like imitating their habits when acting.
During the series running, Chopper showed his habits tend to easily believe in the things he just heard. He just believes when Nami lies to zombie Lola if he is a boy. Usopp was very fond of teasing him, especially making him a casual victim with false stories. When returning to Sabaody, Chopper was thoroughly fooled by the appearance of fake Zoro and fake Sanji.
Source : WIKIA ONE PIECE