Thornton takes ownership of Buck from a trio of ignorant stampeders, intent upon making a dangerous river crossing. Buck refuses to cross, despite a vicious beating. Thornton recognizes the dogs intelligence and strength. He steps in to claim the dog and nurses Buck back to health. But Buck is forever changed by the treatment he has received at the hands of other men.
Jack London spent a year living in the Yukon and drew heavily upon his experiences there while writing the book. He later said, "It was in the Klondike that I found myself."