Tony Tony Chopper is a fictional character in the anime and manga series One Piece.

History

Chopper was originally an ordinary reindeer with the slight oddity of a blue nose which caused other reindeers to treat him as an outcast (always making him follow the herd from far back), but when the young reindeer ate the Human Human Fruit (Hito Hito Fruit in the Japanese version), he was ostracized from his herd and struck out on his own. Unfortunately for Chopper, his attempts at communicating with the humans on Drum Island proved disastrous, and he was shot by villagers who mistook him for a monster. Luckily, though, he was rescued by the quack Dr. Hiriluk (Hiruluk in the Japanese version), who named him and took him in as his friend and 'assistant.' Although his deeds were of dubious medical value, Dr. Hiriluk became Chopper's role-model. Hiriluk taught Chopper his philosophy on life, his strong faith in the Jolly Roger as a symbol of strength against all odds, and his belief in a panacea that would one day cure all illness. The two went from house to house, administering their "cures" in a country where all doctors not sanctioned by King Wapol were banned.

When Hiriluk's health took a turn for the worse, however, Chopper found himself left out in the cold once again as the old man (apparently) didn't want Chopper to watch him die. But once Chopper found out what was going on, he determined that he would find something to cure his mentor and only friend. He soon found what he was looking for: a special kind of mushroom with a skull-and-crossbones prominently displayed. Remembering what he overheard by some villagers that certain special type of mushroom can heal every illness, Chopper steals Hiriluk's favorite medical book to find the miracle mushroom. Chopper's arduous journey was a success, although he risked his life and suffering almost fatal injuries (left horn had broken).

Hiriluk overwhelmed with tears of gratitude, eats the mushroom to show his love and appreciation to Chopper, but Chopper would later find out from Dr. Kureha that he had given Dr. Hiriluk a fatal dose of poison. But Hiriluk was not to live much longer, anyway. Declaring that he had had a wonderful life, he committed suicide by blowing himself up outside of Drum Castle (before being killed by the poison, for Chopper's sake), where he wanted to heal the sick before he died. As per Hiriluk's last wish, Dr. Kureha (the last remaining doctor not owned by the Government) took Chopper in and taught him real medicine for the next 6 years. Chopper worked as hard as he could, in order to one day create the panacea that he longed to have saved Dr. Hiriluk with.

However, Chopper's isolated life in Drum Castle (which he and Dr. Kureha annexed after the King fled) would one day come to an end with the arrival of Monkey D. Luffy and his Pirate crew. Chopper, naturally distrustful of humans, was not pleased (nor was this helped by Luffy and Sanji's shared desire to cook and eat him). But when Chopper showed both his medical prowess and his skills in battle against the returned forces of King Wapol, Luffy offered (forced) him the (as-yet unfilled) position of Ship's Doctor in his crew. While Chopper was at first unwilling to leave, he remembered Dr. Hiruluk wishing Chopper to sail around and seeing the world on his own and with his desire to broaden his medical horizons, he decides to join Luffy and his crew. Fleeing the castle with the Straw Hat Pirates, Chopper was given a send-off of gigantic proportions: Kureha had turned the snow into pink "cherry blossoms," the very same that Hiruluk had researched over 30 years that would one day, cure the people of Drum of their "sickness of the heart," passed to Dr. Kureha as one of his last request before death. Overcome with tears, Chopper bade a fond farewell to his birthplace and mentors, setting out to sea for the first time in his life.


Life at Sea
Abord the Merry Go, Chopper was quickly thrust into battle against the forces of Baroque Works, on the island of Alabasta. While unused to the heat, Chopper was instrumental in getting the assistance of the island's animals and defeating the Mr. 4 / Miss MerryChristmas team.

As time would go on, Chopper would form an especially strong bond with the ship's Marksman and Liar, Usopp. The naive reindeer would often get taken in by Usopp's fibs, believing him completely. But despite this oddity, the two came to be a sort of "team," supplementing each other's skills in battle and generally becoming the best of friends. On his own, Chopper became a vital aspect of the crew, treating their injuries and keeping their spirits up with his constant amazement at the variety and wonder of the world.

As of late, Chopper has become somewhat conflicted in his role. While he continues to be faithful to his crew and dispense valuable medical assistance, he was badly shaken when Usopp (arguably his closest friend in the group) chose to leave. Panicked and saddened by this development, it was all Chopper could do to leave behind some medical supplies to treat his former crewmate's wounds, while he followed his captain into the Venetian-styled city of Water Seven. He was instrumental in saving both Iceburg and Pauly from the destruction of Galley-La Company's headquarters, and afterward expressed his determination to help retrieve Usopp from the clutches of the World Government organization CP9. While Sanji succeeded in retrieving both Usopp and Franky the ship dismantler, Usopp is currently in the guise of SogeKing (a sharpshooting hero of Usopp's own invention, from the Island of Snipers). Despite the others immediately seeing through "SogeKing," Chopper and Luffy do not recognize SogeKing as actually being Usopp (with Chopper even asking for his autograph). Usopp does not seem to want Chopper to know the truth yet, and guards his disguise carefully. Only time will tell what role Chopper will play now that the Straw Hat Pirates have reached Enies Lobby and prepare for the final showdown with CP9.


Powers
As previously mentioned, Chopper ate the "'Human-Human Fruit'", or "Hito Hito no Mi". This is a "Zoan"-type fruit which gives the one who eats it three base transformations:


Walk Boost: This is Chopper's form as a normal reindeer, useful for general travel on foot. Called "Walk Point" in the Japanese.
Brain Boost: Chopper's usual 'Super Deformed' look, with a small body and large head. He is smarter in this form, and also inexplicably cute. In addition he can scope out an enemies weakness in this form while he is under the influence of a Rumble Ball. In the Japanese version it is named "Brain Point".
Heavy Boost: Chopper's "monster" form, which gives him a human-like appearance and height. He uses this form to help steer the ship. Called "Heavy Point" in the Japanese.

Additionally, Chopper has added on to these by use of the "'Rumble Ball'", which gives its user several more transformations for a limited time:

Jumping Boost: Chopper keeps his reindeer legs in a human-like form, which allows him to jump long distances. "Jumping Point" in the Japanese.
Arm Boost: Chopper's fore-hooves become extremely muscular in his humanesque form, powerful enough to inflict a great amount of damage. In the Japanese version, this is called his "Arm Point"
Horn Boost: Similar to Walking Boost, but Chopper's forelegs get bulkier and his horns get larger and sharper. In the Japanese version it is called "Horn Point".
Guard Boost: Chopper's fur grows out and becomes an impenetrable shield against outside attacks. He looks like an overgrown Chia Pet in this form. In the Japanese version it is named "Guard Point".

Misc. Information
Chopper is currently about 15 years old.
Chopper can understand and speak to other animals, which comes in handy at various points during the story.
The name "Tony Tony Chopper" is partly a play on "Tonakai" ("Reindeer"), and partly on the idea that his horns look like they could chop down trees.
Chopper's reindeer appearance often comes in handy. Enemies will usually assume he is just a pet when they haven't actually interacted with him. This was especially useful in Alabasta, when he played an instrumental role in Sanji breaking the others out of Rain Dinners.
Most people call him Chopper, however Nefertari Vivi called him "Tony-kun", and Nico Robin refers to him as "Doctor".
Chopper takes his crewmates as role-modells trying to act like them.
One of Choppers habits is his reverse cartoon peek where he's standing on a wall or doorway and peeks at people, trying not to be seen hismelf. Unfortunately he's not hiding his body behind the wall but hides the peek eye so his body is visible and only one half of his face is hidden.
Chopper does tend to overreact a bit when someone is in need of help. He is prone to freak out, yelling for a doctor just to realize that he is one.