Thornton is one of the main human characters in the book. He is important in the life of Buck, but we don't know much about him. In one sense, Thornton's role in the story is to help us learn more about Buck – Thornton’s there so we can understand this mysterious call of the wild and why Buck feels torn about whether to stay with humans or go into the wild.
Thornton is both the greatest thing that’s ever happened to Buck and the one thing holding back from his true destiny as a wild dog pack leader. One the one hand, Buck is devoted to Thornton in a way that he is not devoted to anyone or anything else – recall how Buck was willing to jump off a cliff for Thornton. On the other hand, Thornton's presence is preventing Buck from going off into the wild and answering "the call" that he hears so often. How do you view Thornton's role in The Call of the Wild? Does he bring out the best in Buck, or does he prevent Buck from realizing his dream? Or is it both?