Explain Buck the protagonist and his situation.

In Jack London's Call of the Wild, Buck is a sled dog who, because of his physical prowess, is taken from the comfort of his home by ruthless dog sellers who beat him into submission with a club.
In the early passages of the book, Buck is described as being a kind, obedient, and generally domesticated dog. One passage of the book reads,

for he was a civilized dog, an unduly civilized dog, and of his own experience knew no trap and so could not of himself fear it

Buck, disassociated with his wild side, finds comfort in being the friend of man. Of course, as the novel continues, and as Buck experiences the wilderness with greater frequency, he finds himself being magnetized to the wild world that surrounds him. Buck's struggle is, essentially, to make the decision between his two possible lives: one of submissive domesticity; and one of complete freedom among nature. Buck's love for his master Thornton is tested by the titular call of the wild.