Who is Mr. Sing from To Have and Have Not and what is their importance?

Mr. Sing is the "smoothest looking thing" that Harry Morgan has ever seen. Sing is a Chinese man and a sharp dresser, who speaks like an Englishman, and also knows some Spanish. Frankie introduces Sing to Morgan when the captain is broke, and Sing makes arrangements to charter Morgan's boat. In the end, Morga kills Sing and throws him overboard.