Who is Buck's primary rival for leadership in the sled team?

Buck's primary rival for leadership in the sled team is Spitz. Throughout "The Call of the Wild," Spitz is established as the lead dog and displays strong leadership qualities, but his dominance creates tension within the team. Buck, as a powerful and resourceful dog, gradually begins to challenge Spitz's authority. This rivalry becomes central to the story, highlighting themes of survival, instinct, and the struggle for power in the harsh wilderness environment. Their conflicts culminate in a decisive showdown where Buck ultimately asserts his strength and cunning, leading to his victory over Spitz and solidifying his place as the leader of the sled team. This dynamic not only drives the plot forward but also serves to illustrate Buck's transformation as he reconnects with his primal instincts.