Perhaps 'king yellowman' is a character from a less - known folklore or a new story being developed. He could be a symbol of something within the story, like a representation of a certain value or a force, but again, without more information, it's all speculation.
Since the name is not a commonly known figure in mainstream stories, he could be a protagonist in a very local or niche story. Maybe he is a king in a fictional land with his own set of adventures and characteristics that are only known within the context of that particular story.
As I said before, without more context, it's hard to determine who 'king yellowman' is in the story. It could be an entirely new character created for a special narrative purpose.