Which character places a bet on John Thornton?

The correct answer is Matthewson, who is a character that represents the competitive culture of the Klondike Gold Rush. He places a bet on John Thornton's ability to successfully handle Buck in a wager against another character. This moment emphasizes not only the betting culture of the time but also the tension and rivalry that can arise in the harsh environment of the Yukon. Matthewson's actions illustrate both the risks that come with trying to profit from the struggles of others and the sense of adventure that defines life during that period.

In this context, the other characters mentioned do not engage in betting on Thornton. Thornton himself is the person being wagered on, while Manuel and the Man in the Red Sweater play different roles within the story, focusing on their own relationships with Buck and the consequences of the dog fighting culture he initially faced. Thus, Matthewson's role in placing the bet is a pivotal moment that encapsulates the themes of power dynamics and survival in "The Call of the Wild."