Brook

Brook is the musician of the Straw Hat Pirates. He is a skeleton the Straw Hats found on board a ghost ship after drifting into the Florian Triangle. He is a Devil Fruit user who ate the Yomi Yomi no Mi and is an undead being brought back into a pseudo-immortal state because of its powers. He fills the role of the long awaited musician that Luffy wanted for his crew since his journey began. Brook is a great lover of music.

Whether it be through happy or sad times, music is what generally keeps Brook going. As a result, his love for music often reflects itself in various other aspects of his character such as in his fighting style wherein the names of his attacks are derived from various musical songs and dances. He gave himself a musical theme so noticeable that while he was alive in his first life, he was called "Humming Brook" by the authorities.
Brook's devotion to music not only helped him to pass the lonely days but also serves as a combat tool. Most of the techniques that he deals out are named after or related to music. One of them even acts as a hypnosis that sends his enemies to sleep, however, this can also affect allies. Due to his musical background, Brook also moves according to the rhythm of music to assist him in battle, and soon became a world famous rock star during the past two years, at which point his records in tone dials were sold in millions and his fans on his final world tour in Sabaody Archipelago were either crying or fainting at his presence.
Brook believes in and has quoted the philosophy "Good things come to those who wait", given the years he spent on the ghost ship, and Laboon's eternal patience.

The concept of Brook, a skeleton musician, had already been thought up by Oda the first time he drew Laboon. Brook's overall design however wasn't finalized back then but the basic idea was kept for a long time until Brook was finally revealed.
In One Piece Green: Secret Pieces was revealed an early concept of Brook. Oda thought about the skeleton Brook back when One Piece reached the Laboon Arc, but only in the Thriller Bark Arc he was introduced.