Who was the short, half-naked man in Buck's dream?

I'm not sure myself but here is one version,

"The hairy man that Buck dreams of is a partner to him, Buck believes that man and dog go together. It may be a representation of Weedon Scott form 'White Fang", another of Jack London's stories."

The physical description of this man makes it clear that he is intended to be an example of prehistoric man: hairy, practically naked, long-armed and short-legged, inarticulate, equipped only with a club. He is a symbol of the primitive, a figure from ancestral memory, a reminder of the time before civilisation. This is of course pertinent to the book as a whole as it details Buck's gradual reversion to primitive life in the cold Arctic regions where man and beast alike fight to survive in a harsh environment. This figure becomes more prominent in Buck's dreams as he becomes ever wilder and more wolf-like. In the end, absolutely no trace remains of his former civilised ways...