As the two previous posts have mentioned, the main character of Jack London's classic novel is Buck--a dog. Buck's narration is one of the most unusual aspects of the novel: an adventure tale told through the eyes of a canine. According to London's story, Buck becomes the most famous dog in Alaska. His part-St. Bernard, part-Scottish Shepherd pedigree makes him larger (at about 150 pounds), more powerful, and more intelligent than all of the other dogs he encounters in the Klondike. His everlasting fame is earned late in the story when he wins his then-master, John Thornton, a large sum of money by pulling a 1,000 pound load and breaking it from the ice for 100 yards--an unheard-of achievement for any sled dog.

As for the main human characters:

JOHN THORNTON.  Buck's final master, Thornton saves Buck from the thoughtless master and newcomer to Alaska, Charles, by cutting him from his traces shortly before the rest of the group and dog team plunge to their deaths through the ice. Thornton is a loving master who treats Buck more as a pet than a worker. Buck comes to love Thornton more than any other man, worshipping him for the humanity that he shows at all times. When Thornton is murdered by Indians, he avenges his master's death by killing many of the group. 

FRANCOIS and PERRAULT.  The mail couriers are among Buck's first masters, for whom he becomes a great dog team leader. They are fair men who recognize Buck's greatness, but they also beat him when necessary. Buck learns to honor "the club" that they use, realizing that a human with a club is all-powerful. Reluctantly, they are eventually forced to sell Buck, knowing that there was "Nevaire such a dog as dat Buck!" 

Although the main character is a dog, this story is neither an allegory nor a fable since Buck does not representent a character type or take on an interpretative role in any way. During his capture and adventures up North, he comes across other characters - dogs, wolves, people. Click on the following reference for a list and short character profile of each.

Yes, you are right - in terms of main character, the novel 'Call of the Wild' by Jack London is confusing when we see that the main protagonist is a dog! There are other characters too of course and they have an important part to play, but the lovely thing about this story is that the story is told through the eyes of Buck,a dog, but the author makes sure that we as readers have lots to identify with too. In terms of breed, Buck is half St Bernard and half Sottish shepherd - obviously we need his 'thoughts' and 'emotions' interpreted for us by the author. At first Buck lives like a lord in warm sunny California, but he gets stolen by a gang rushing North to the Klondike in the hope of discovering their fortunes in gold. They like the look of his warm shaggy coat and his qualities are ideally suited to the harsh life of a Northern winter.....