He is Tom's master in Kentucky. He is also described as being off the good characters in the novel. Shelby is characterized as a kind of slave owner, who cares about other people without paying attention to the color of the skin. You know, he is the stereotypical Southern gentleman. When Shelby experiences a financial crisis because of gambling debts, he sells Tom and the little boy Harry to save his plantation. And this shows him from the very good and gentle side.
Arthur Shelby in the Essays