The One Piece series is known for many things, including its exceptional character backstories. These backstories are always sincere and raw, and every time a new one pops up, we think it can't get any better than the previous one, and yet it does.

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From child slavery to the loss of loved ones and tragic environmental conditions, One Piece's backstories spare nothing, and these are just some of the best that Oda has given us.
9
Trafalgar Law
Trafalgar D. Water Law, the Surgeon of Death, revealed his past during the Dressrosa story arc, quite some time after he was first introduced to us in Saobody. The wait was worth it, though, as we get a lot of information about him, Doffy, and Doffy's brother, Corazon.
During his story, we find out that Law had metal sickness and had to fight to be the last survivor of his village. He was taken in by Doffy and his crew and ended up befriending Corazon, Doffy's brother. Corzaon tries his best to heal Law and ends up sacrificing himself to let Law live and give him the Op Op fruit.
8
Stream
Brook is the adorable, reliable and slightly perverse skeletal musician of the Straw Hats, which is something Luffy has always wanted. He is discovered alone on an abandoned ship at the beginning of Thriller Bark, and as the arc progresses, we learn how this came about.

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Brook was the musician and captain of the Lumbar Pirates, a close-knit crew. Brook ate the Yomi Yomi no Mi, which he didn't know would bring him back from the dead once. The Rumbar Pirates died in battle, and Brook's soul eventually found its way back into his body, which was now a skeleton, as he wandered the Florian Triangle alone for decades.
7
Great Mom
Big Mom is one of the Yonko, the four emperors of the sea, some of the strongest pirates in the world. Big Mom isn't the only one we have a backstory about, but she definitely has a sad and, frankly, disturbing backstory.
Charlotte was an enormous child, who at five years old even surpassed adults. She was not a member of the giant species, but she might as well have been, and due to her size and propensity for causing unintended harm, she was orphaned on Elbaph to be taken in by Mother Carmel. During a festival, she was so excited and consumed with hunger after eating delicious food that it is heavily implied that she ate all the other orphans and Mother Carmel in a blind hunger-induced frenzy. That idea has some of the darkest implications the story has had to date.
6
Nami
The cat-thief navigator of the Straw Hats, Nami is one of the original members and the first lengthy backstory we've gotten, and boy, does it hit hard.
Nami lived in Cocoyasi Village with her adoptive sister Nojiko and mother Belle-mere. They lived poor but happily until the island was attacked by Arlong and his crew; Belle-mere was killed while trying to protect her daughters, and Nami was enslaved by Arlong and forced to draw maps. She also mentions that on her tenth birthday her gift would be to be freed. This all culminates in Nami using a knife in the present to try to cut out Arlong's pirate tattoo from his skin and begging Luffy to help him, to which he eagerly responds that he will, along with Zoro, Usopp, and Sanji.
5
Boa Hancock
Boa is a member of the Kuja clan and captain of the Kuja pirates. Although she is now a successful pirate, empress, and warlord of the sea, she wasn't always so lucky.

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As a child, Boa and her sisters were with the Kuja pirates when they were captured and sold to the World Government as slaves. Boa was forced to eat her devil fruit to entertain her masters, and she and her sisters endured unspeakable horrors for years until they were freed by Fisher Tiger and his revolutionaries.
4
Oden
Kozuki Oden gets perhaps some of the longest backstory/flashbacks in the series. We spend multiple chapters seeing what he was doing with the Whitebeard Pirates, and everything before and after leading up to the current timeline and what Momonosuke knows.
And Oden definitely wins the man of the century award. He loved his family and his people, constantly sacrificing his dignity and reputation to keep the people of Wano safe from Oroch. During his execution, in which he and his servants were to be executed in a boiling pot, Oden saved them by holding them all raised above his head until he died and the boiling water ceased.
3
Sanji
Sanji is the chef of the Straw Hats and one of the “Wings of the Pirate King”. We had some backstory for him in the beginning, when he was trapped with Zeff on an island and Zeff gave him all the food, but the rest of his story is revealed during Whole Cake Island.
We learn that Sanji was the misfit son of the Vinsmoke family, as their father, the Judge, wished for all of them to be genetically enhanced. Their mother, Sora, did not want this and took a drug during her pregnancy that prevented Sanji from achieving these improvements like his brothers and sisters. This also led to Sora being extremely ill and bedridden, and Sanji prepared meals for her, which were the only things she would eat. Sanji was continually bullied by his brothers and failed so badly in their training that the judge placed him in a cell and with an iron mask.
2
Robin
Robin is a fan-favorite member of the Straw Hats, and for good reason. She's beautiful, kind, funny, powerful, and has an incredibly heartfelt and engaging backstory.
She grew up on the island of Ohara, the leading knowledge capital in the world. She grew up despised and abused by her mother's sister's husband, Roji, and because of this and her devil fruit abilities, she was not allowed to hang out with other children her age or attend family events. Eventually, she found a friend in the Giant, Saul, who taught her to laugh and be happy despite her circumstances. As his mother and the other historians on the island researched the Void Century, they were targeted by the world government and the island was subjected to a Buster Call. The island was decimated to pieces, with Saul sacrificing himself to save Robin and Aokiji, leaving her to escape on a raft. She ran away with the typical laugh Saul taught her while she cried.
1
Kuma
Kuma has long been one of the most intriguing and mysterious characters in the series, first appearing as an antagonist and then proving to be a solid ally for our Straw Hats. His reveal of the backstory during the Egghead arc was tragic and touching, and shed a whole new light on the character.
Kuma was raised as a slave to the World Government, as he is a member of the Buccaneer race, who Jaygarcia Saturn claims were born to be slaves. Eventually, he escapes, befriends future revolutionaries, and falls in love with Ginny, with whom he has Jewelry Bonney. Throughout his life, Kuma has been through incredible hardship, slavery, love and loss, stripped of his humanity and used as a tool, all for the good of his world and his daughter.

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