appearance
Most of the time, Chopper is a toddler-sized human/reindeer hybrid, his devil fruit abilities allow him to change his appearance depending on the situation. Chopper's reindeer appearance often comes in handy, as enemies will usually assume he is just a harmless pet when they haven't heard him speak. This was especially useful in Alabasta, when he played an instrumental role in Sanji breaking the others out of Rain Dinners. Chopper's left antler has a metal plate wrapped around it at all times, from being broken in a fight when he was younger. Chopper also has a remarkable feature that no other reindeer have, and that is blue nose, while normal reindeers have black ones.
A running gag is that various characters in One Piece think Chopper is a tanuki (raccoon-dog, often simply translated as "raccoon") whilst in his Brain Point form. This is a play on the similar word "tonakai," the Japanese word for reindeer, from which the "Tony" in Chopper's name is derived. His heavy point form likewise is mistaken for a gorilla or an abominable snowman.
Oda has stated that he uses the color pink to represent Chopper, and (Oda was answering the questions as Chopper) for his smell, "how am I supposed to know?"
personality
Chopper is naive and highly timid often acting as a child because he doesn't know any better. Chopper is more or less on a journey to define himself, seeing almost anyone on his team as a role model and in some cases, imitate their behavior, especially Usopp. When Chopper recognizes someone needs medical attention he often will start to panic and scream for a doctor, just to realize that he is one. He would rather run and hide then fight, but becomes more courageous when others are there to support him.
Another one of Chopper's habits is his reverse cartoon peek, where he stands behind a wall or a doorway and peeks at people, trying not to be seen by them. Unfortunately he's not hiding his body behind the wall, as a result his body is visible and only one half of his face is hidden.
He is an upright friend and companion who will try anything to overcome a task given by his team. He still has a feeling of distrust for humans for his youth and will often outright insult and claim that compliments don't make him happy to a human who compliments him while obviously being happy about it (he starts to smile and also dances a little).
In the group, Chopper often fools around with Usopp and Luffy for laughs and is also a thankful listener to Usopp's lies, most of which he really believes, at least for a short time. Robin calls him "Doctor-San" which makes him dance in joy. Sanji originally wanted to cook Chopper and jokingly wants him to joins as "emergency food supply" continues to refer to him as "the emergency food supply" to tease him but considers him a friend. Chopper originally wasn't hired to be the ship's doctor by Luffy, but just for being a "cool reindeer that can transform".
Back on Drum Island, the people have come to accept his help in defeating Wapol, even though originally they were afraid of him. Chopper has also gained Dalton's respect.
Chopper initially idolized Dr. Hogback, but after learning of his disregard for human life and coming into conflict with him and the rest of Gecko Moria's forces, he declared that he no longer considers him a doctor. He is wanted by the Marines, albeit with an extremely low bounty which is 50 belli.
Chopper's real family is a herd of Reindeer, who abandoned him for being different. Initiallly estranged for being born with his blue nose, he is further abandoned after eating the Hito Hito no Mi, which gives him an "unreindeer-like" humanoid form. He eventually found his paths intertwined with them during his days with Hiriluk and was beaten up. However he was able to pass through them despite this and achieve his goal at the time.
Hiriluk was Chopper's mentor who took him in and became his "father". They had a close relationship with each other, and had formed a deep bond despite their almost constant arguing with each other. Despite his time spent with the superior Doctor Kureha, Chopper refers to Hiriluk as "the greatest doctor in the world."
Though neither family nor claiming to have adopted him, Doctor Kureha is his mentor. While she often hides her feelings towards him she considers him like a "son" to her. She is happy to know he is currently well.
[center]abilities and Power
Basic Transformations As previously mentioned, Chopper ate the "Human-Human Fruit". This is a "Zoan"-type fruit which gives the one who eats it three basic transformations:
* Walk Point: This is Chopper's form as a normal reindeer, useful for general travel on foot. It is also in this form where his olfactory senses are at their highest. As a result, Chopper often make use of his default form for tracking purposes, though certain scents seem to dull his sense of smell. Called "Sprint Boost" in the English dub and "Limb Boost" in the English manga.
* Brain Point: Chopper's usual 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. This is also the form where he does his best thinking because he can utilize both human intelligence and reindeer sensitivity at the same time. In the English version, Brain Point is called "Brain Boost".
* Heavy Point: Chopper's "human" form, which gives him the form of a tall, muscular ape-man. He uses this form to help steer the ship. This form imbues Chopper with super-human strength. In fact, when he first used this form against Luffy and Sanji (who were trying to catch him and eat him) Chopper was able to knock both Straw Hats out at the same time. This form is called "Heavy Boost", and his voice becomes deeper, while in the Funimation English dub (and manga) it's called "Weight Boost" and his voices stays the same(such as in the Japanese version).
Rumble Ball Transformations Additionally, Chopper has added on to these by use of the "Rumble Ball", which gives its user several more transformations for three minutes by 'distorting the wavelengths of transformation':
* Jumping Point: Chopper keeps his reindeer legs in a human-like form, which allows him to jump long distances. "Jump Boost" in the English version.
* Arm Point: Chopper's second most powerful form, his fore-hooves become extremely muscular in his human-esque form, allowing him to deliver devastating punches with his front hooves. In the English version, this is called "Arm Boost."
* Horn Point: Similar to Walk Point, but Chopper's forelegs get bulkier and his antlers become larger and sharp. In addition, Chopper has human fingers in this form. In the English version it is called "Horn Boost".
* Guard Point: 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 English version it is named "Guard Boost".
It is likely that Chopper will discover other forms that he can transform into. It has recently been revealed that Chopper can't eat multiple Rumble Balls back to back within 6 hours or otherwise he'll lose control of his transformations.
* Monster: It seems that the consumption of three Rumble Balls in under six hours created a new Point in which he is standing similar to Heavy Point, but possesses an oddly misshapen head and antlers, as well as an incredible (likely more than twenty feet, or about the size of an office building) increase in height and strength. Chopper's fur is lengthened in this form. Chopper also loses all consciousness and goes completely berserk in this form. Also, this form appears to be a combination of all of Chopper's transformations, not including Brain Point and Arm Point (Heavy Point stance, Walk Point speed, Horn Point horns, Jump Point legs, and Guard Point hair). Doctor Kureha told Chopper that after he consumed three Rumble Balls for the first time, he leveled an entire village on Drum Island while on this form. Kureha also commented on this form being that of a true monster; a danger to friend, foe, and even Chopper himself. According to Zoro's observation, this transformation appears to be lethal to Chopper, as the amount of energy needed to maintain the form is too much for his little body to handle. The only known way to end this form is by placing Chopper into the sea.
Other Abilities Chopper being the doctor of the crew, has a large knowledge of medicine and medical drugs as well as the preparation of remedies and ointments from regular fruits, roots and vegetables found on most islands. Most of this he learned during his apprenticeship under Dr. Hiruluk and Dr. Kureha. In addition to the transformational advantages that Chopper's Zoan forms afford him in battle, he has also been known to employ wrestling-type moves (i.e.pinning down an opponent,or smashing them to the ground by means of a supplex) from time to time. His extensive knowledge of the bipedal anatomy also proved useful when the Straw Hats were trying to bring down Oz, during which time, Chopper formulated several theories on where it was best to target the colossal adversary. And while naive, he can be quie as strategist, as seen on his fights against the Mr. 4 pair and Gedatsu.
Chopper, who originally was an animal, is also capable of speaking to and understand other animals, which came in handy on various points of the story.
Chopper was originally a reindeer with the slight oddity of a blue nose, which caused other reindeer to treat him as an outcast (always making him follow the herd from far back). However, when the young reindeer ate the Hito Hito no Mi, he was even more ostracized from his herd (and with the increase in intelligence granted by the fruit, now acutely aware of it) and struck out on his own. Unfortunately for Chopper, his attempts at communicating with the humans on Drum Island proved disastrous, he was shot by villagers who mistook him for the Abominable Snowman. Luckily, though, he was rescued by the quack Dr. Hiruluk (Hiriluk in the English version), who named him and took him in as his friend and 'assistant.' Although his deeds were of dubious medical value, Dr. Hiruluk became Chopper's role-model. Hiruluk taught Chopper his philosophy on life (that all diseases could be cured) and his strong faith in the Jolly Roger as a symbol of strength against all odds. The two went from house to house, administering their "cures" in a country where all doctors not sanctioned by King Wapol were banned.
When Hiruluk's health took a turn for the worse, Chopper found himself left out in the cold once again as the old man didn't want Chopper to watch him die. But once Chopper found out what was going on, he was determined to find something to cure his mentor, his one and only friend. He soon found what he was looking for: a special kind of mushroom with skull-and-crossbones prominently displayed in the medical book, unaware of what that sign really meant due to Hiruluk's praising of pirates. Remembering what he overheard by some villagers that a "certain" type of mushroom can heal every illness, Chopper steals Hiruluk's favorite medical book to find the miracle mushroom. Chopper's arduous journey was a success, even though he risked his life and suffered many injuries, such as a broken left horn.
Hiruluk overwhelmed with tears of gratitude, ate the mushroom to show his love and appreciation to Chopper, but Chopper would later find out from Dr. Kureha that he had given Dr. Hiruluk a fatal dose of poison. But Hiruluk was not to live much longer anyway. Declaring that he had a wonderful life (in the english dub he declares he is a doctor), he committed suicide by blowing himself up outside of Drum Castle (before being killed by the poison, for Chopper's sake). As for Hiruluk's last wish, Dr. Kureha (the last remaining doctor not owned by King Wapol) took Chopper in and taught him 'real' medicine for the next 6 years. Chopper worked as hard as he could, in order to become a doctor like his idol, Hiruluk..