Boa Hancock lived most her life with the Kuja Pirates up till age twelve when during sailing she and her two sisters were captured by slavers. These slavers then sold her and her sisters off to the Celestial Dragons. During this time she suffered great pains for four years, during this time the Celestial Dragons also fed her the Mero-Mero no Mi as entertainment. This torture went on until one day captain of the Sun Pirates, Fisher Tiger caused a riot in Mariejois, to free all slaves(though previous motive was freeing fishmen).
Hancock was left alone with her sisters soon rescued by Elder Nyon, Silvers Rayleigh, and Shakuyaku. When brought home she still had the mark of the Celestial Dragons on her back, choosing to hide it along with her devil fruits. Passing her powers off as a curse of killing gorgons, her sisters did the same. They were then named the 'gorgon sisters'.
Though freed, the experience she went through at Mariejois had corrupted her, leaving her a cold-hearted person, suppressing any feelings being uncaring to most everyone especially men, and even her own people.
At eighteen years old she she was crowned empress of Amazon Lily, and gained a reputation prompting the World Government to place an 80,000,000 belly bounty on her. To protect her people, she accepted membership to the Shichibukai. Her epithet being "Pirate Empress".
Hancock is known as the most powerful of the Kuja Pirates, and is physically quite powerful. She managed to take down a Pacifista with not much effort.
Hancock possesses the Mero-Mero no Mi (Love-Love Fruit). This grants her the abilities to turn anyone who feels attraction towards the user to stone.
Hancock has show two types of haki, Busoshoku and Haoshoku haki.
Her level of Busoshoku has shown to be quite powerful being able to kick Smoker away from Luffy. Her Haoshoku hasn't been shown, but it is known she has it.