Who are Hal, Charles, and Mercedes?

Hal

A young man of nineteen or twenty who purchases Buck and his team once they have used up their usefulness to the government. He has ambitions to find gold, but his incompetence and laziness are out of place in the harsh environment. He has no understanding of the dogs, and mistreats them terribly.

Charles

Hal's brother-in-law, a weak figure who does not say much. He basically follows Hal around and does what he is told.

Mercedes

Sister of Hal, wife of Charles. She is exceedingly self-centered, and spends most of her time crying and complaining.