Herbert Dolls was a member of the crew of the Karaboudjan.
Somehow he made contact with the Japanese police and intended to denounce the unlawful activities of the ship. He just had time to write a track on a piece of paper and was discovered and murdered by his crewmates.
He was a key in The Crab with the Golden Claws, since the discovery of his body was what started the investigation of the case, and the piece of paper, later found by Tintin, was what helped them discover the involved in the plot.
Trivia
In The Crab with the Golden Claws book his body is found by the police and referred as "drunken man". In The Crab with the Golden Claws Episode is stated his full name, but he is referred as "drowned man".