How was Buck's life with John Thornton different from his life with his other masters ?

John Thornton and Buck's connection goes far beyond the working relationship that Buck had with Francois and Perrault. He respected those men for their understanding of dogs and of nature, but he had no great affection for them. John Thornton is "the ideal master," for he understands Buck without difficulty or confusion. Buck loves him because he shows his need for Buck, repeatedly demonstrating that Buck can help him in ways that others can't.