In terms of characterization, Rainsford is a dynamic character since he changes during the narrative. For, in the exposition during his talk with Whitney, he is a man convinced of his opinions, giving no credence to the viewpoints of his friend. First, when Whitney suggests that the hunted animal understands fear, "the fear of pain and the fear of death," Rainsford answers, "Bah! They've no understanding." Then, when Whitney suggests that there may be something ominous out at sea, Rainsford discounts the "sudden dread" of the old Swede and Whitney: "Pure imagination."
Later, after he is captured and dining with General Zaroff, Rainsford is appalled when Zaroff suggests the excitement of hunting other men. The general hints that Rainsford may have done just this: "Surely your experiences in the war--" but Rainsford "stiffly" cuts the general off, saying he did not condone "cold-blooded murder."
Further in the plot, Rainsford changes because he attains the "understanding of fear and death" as he himself becomes prey for Zaroff. Then, too, he certainly feels the "certain dread" which he has earlier discounted. And, finally, he acts in the manner that he has earlier condemned. He confronts Zaroff as "an animal at bay" and fights for his life against another man. When the author writes, "He had never slept in a better bed, Rainsford decided," the reader must conclude that Rainsford has killed Zaroff "in cold blood" or he would not be alive. Thus, the resolution of the conflict finds Rainsford a different man from what he is at the beginning.
Rainsford could be considered the protagonist character in this story. A professional big game hunter, he becomes stranded on General Zaroff's Ship-Trap Island, and becomes the same kind of prey he once hunted. His empathy for the game changes as the story progresses.
In the end, he does eventually win in "The Most Dangerous Game," as its conclusion tells us that Rainsford had never slept in a more comfortable bed (the general's). It is implied that Rainsford killed him. Overall, Rainsford's character is central to the plot of the story, and we view events in the story largely from his perspective. These and other factors make him the protagonist.