Who saves Buck but is later killed by the Yee-hats?

The choice of John Thornton as the character who saves Buck and is later killed by the Yee-hats is correct. John Thornton is a pivotal character in "The Call of the Wild." He represents kindness and the bond of loyalty and love that Buck craves after his harsh experiences in the wild. Thornton saves Buck from a dangerous situation, demonstrating his compassion and bravery. Their relationship exemplifies a deep connection between human and dog, with Buck finding a sense of belonging and care in Thornton.

Tragically, Thornton's life is cut short by the Yee-hats, which further emphasizes the themes of survival, violence, and the impact of nature on life in the wilderness. This event marks a turning point for Buck, highlighting both the dangers inherent in his world and the loss of the one person who truly understood him.

The other characters listed do not fit the role of rescuer in Buck's life. Hal and Charles are figures representing the harsh, irresponsible treatment of Buck and the other sled dogs, while Joe is a character that, although present in Buck’s earlier life, does not have a major impact akin to Thornton’s.