Brook is a major character from the manga and anime series One Piece, joining the Straw Hat Pirates as the crew's musician. He is a living skeleton, a unique state resulting from consuming the Yomi Yomi no Mi, a Paramecia-class Devil Fruit also known as the Revive-Revive Fruit. This fruit grants its user a second chance at life after death. Brook died decades before his introduction, and by the time his soul found his body, it had decayed to nothing but bones, leaving his distinctive afro as the only remnant of his former appearance.

Before his current life as a skeleton, Brook was a human from West Blue who served as the leader of a kingdom's surprise attack squadron before becoming a pirate. He joined the Rumbar Pirates as a musician and swordsman, eventually becoming their captain after the previous captain fell ill. During a voyage through the Florian Triangle, the entire crew was killed in a battle where they were attacked with poisoned weapons. As the last surviving member, Brook played a final performance of the song Binks' Sake with his dying companions, a memory he preserved in a Tone Dial hidden inside his skull. Decades later, his shadow was stolen by the Warlord of the Sea, Gecko Moria, which forced him to remain in the fog-covered Florian Triangle until he was freed by the Straw Hat Pirates.

Brook's personality is a blend of gentlemanly pretensions and eccentric, childish behavior. He speaks politely, often using honorifics, and attempts to maintain an air of decorum, but his long isolation has severely eroded his social graces. He has atrocious table manners, is known for being flatulent after meals, and has a notorious habit of asking female crew members, particularly Nami and Robin, to show him their underwear. He laughs distinctively with a cry of Yohohoho and has an endless fondness for skull jokes, often commenting on his lack of eyes, stomach, or other organs. Despite his perversion and goofiness, Brook is deeply loyal, courageous, and wise, often using his many years of experience to offer guidance to his younger crewmates. He is also easily frightened by ghosts and monsters, ironically reacting with terror despite his own undead appearance.

Brook's primary motivation is to fulfill a promise made over fifty years ago to a whale named Laboon, who was left behind at Reverse Mountain when the Rumbar Pirates first entered the Grand Line. He treasures his afro because he fears Laboon will not recognize him without it, now that he is only a skeleton. This driving goal led him to join the Straw Hat Pirates, as their journey would eventually allow him to circle the world and return to Laboon. Within the crew, his role is the musician, a position captain Monkey D. Luffy had sought since his journey began. Beyond entertainment, Brook serves as a combatant and swordsman, often pairing with Roronoa Zoro in battle, though his fencing style is lighter and faster, based on iaido and thrusting attacks, in contrast to Zoro's heavier, slashing style.

His key relationships are defined by profound loyalty. He is deeply grateful to Luffy for freeing his shadow and follows him with the same devotion he once showed his original captain, believing Luffy will become the Pirate King. He shares a bond with Franky, who helped convince him to reveal his past, and has a mutually respectful relationship with Robin, as they both hail from West Blue. While he constantly teases Nami, she trusts him with tasks like navigating the ship, and he has proven a reliable ally in battle, such as during the Whole Cake Island arc where he bravely faced Big Mom.

Throughout the story, Brook develops from a lonely, isolated soul who had spent five decades adrift without human contact into a cherished and integral member of a found family. He learns to cope with his profound past losses through music and humor, embracing his second chance at life with zest and joy. His abilities have also matured significantly. While he was always a skilled swordsman capable of incredible speed, light-footed enough to run on water, his powers expanded to allow him to manipulate his own soul. He can project his soul from his body to become intangible, fly, and phase through solid objects for reconnaissance. He also learned to channel the chill of the underworld through his sword, Soul Solid, allowing him to freeze opponents and the surrounding environment, a power he uses to great effect against homicidal homies and even emperors of the sea. His musical talent remains central to his identity, using his violin or guitar to play melodies that can soothe, hypnotize, or directly attack the souls of his listeners.