The Rumbar Pirates are a long dead pirate crew from the West Blue. They were first mentioned by Crocus as the group of pirates who brought Laboon to the Twin Capes.
50 years before the beginning of the main storyline, the Rumbar Pirates travelled in the West Blue. One day, they found a baby whale following them. Seeing he was alone and sad they decided to play music to/for him, in order to cheer him up. The next day they thought he was gone but they found him again. Seeing he still followed them they decided to play for him again and this time allowed him to follow them seeing how cute he was. While feeding him some bait it was revealed that Brook had named him Laboon.
The crew’s strength took them far into the Grand Line, where they experienced its cruel sea and unpredictable weather. Days went by, and at some point after coming out of a certain forest, Yorki, their captain, and several of the crewmembers had contracted an incurable disease. Deciding no one else should be infected, Yorki traveled away with the sick crewmembers on their ship and hoped to pass through the Calm Belt. It was at that point most of them died.
However, the Rumbar Pirates met their end upon entering into the Florian Triangle. A good number of the crew survived the attack, albeit barely, but since the enemy had tainted their weapons with poison and the Rumbar Pirates’ doctor was killed in the attack, the survivors were slowly dying. Knowing that he had eaten the Yomi Yomi no Mi, Brook suggested to his crew that they should play one last song that would be recorded on a Tone Dial that they had previously bought from a merchant. Since he would be revived after death, Brook promised them that he would take the Dial and play it for Laboon to hear. Overjoyed with Brook’s proposal, the remaining Rumbar Pirates mustered what little strength they had and started singing their favorite song for the last time.
Though joyful at recording their song, the remaining Rumbar Pirates slowly succumbed to the poison and died one after another. They each fell with smiles on their faces until only Brook was left all alone. With a heavy heart, Brook continued playing alone until he too succumbed to the poison and died.
After a year of searching, the soul of Brook found the Rumbar Pirates’ ship and his body, which had decomposed to bones. Resurrected as a skeleton, Brook put his comrades’ remains in coffins. However, Brook remained ever aware of his crew’s inability to keep their promise to Laboon.
The first ship used by the Rumbar Pirates was relatively regular sized, and made its debut in a flashback in Chapter 103 and Episode 63. It had the bull skull from the Rumbar Pirates’ Jolly Roger as its figurehead (originally in the manga and anime, the figurehead was maneless).
The second vessel the Rumbar Pirates used after they lost half of their crew made its debut when Brook himself used it to sail around the Florian Triangle.
Despite being wiped out for about half-a-century, the Marines kept track of the crew’s information, as they managed to trace Brook’s connections based on the past bounty poster.