Buck's the alpha dog. The top dog. The big dawg.
And no, we're not being subtle (that wouldn't be in the spirit of London's novel, after all). Buck's an actual d-o-g. He's a canine. And he's our hero.
But put aside any expectation of Buck being the protagonist of a novel by humans and for humans because of his human tendencies. Far from it—Buck's the star of the show because he's a dog that just gets doggier.
But it’s easy to forget he’s not a person (aside from the whole dragging-a-sled-through-the-frozen-North business). That’s because we’re in his head. We never see dialogue-style quotations around Buck’s thoughts, so this isn’t quite Homeward Bound, but Buck is personified in a Lassie sort of way. He has emotions, desires, motivations, the works.
Just check out this passage:
The snow walls pressed him on every side, and a great surge of fear swept through him—the fear of the wild thing for the trap. It was a token that he was harking back through his own life to the lives of his forebears; 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. The muscles of his whole body contracted spasmodically and instinctively. (2.12)
That's not only a visceral passage (you can feel the cold of the snow and Buck's muscles "contract spasmodically); it's also a super-psychological passage. We get Buck's animal fear (trap = no bueno) and we get his pretty advanced-level reasoning of that fear (he knows he's a pampered pooch and doesn't know from the fear of traps...so it must be a fear that predates his birth).
And this dynamic combo of emotions and psychologizing is why we can empathize with Buck as our main character even though he’s got four legs—after all, he seems more human than a lot of fictional humans we could name (*cough Christian Gray *cough cough).
But who is Buck, really? What kind of dog is he? Aside from his physical prowess, Buck's distinguished by his ability to learn and adapt. He goes from being the new kid on the block to the head of the sled team, ousting another alpha dog on the way. By the end of the story he’s a force to be reckoned with.
You're a good dog, Buck. Yes you are.
Of course, the most fascinating part of Buck is his struggle with The Big Question: would I rather kill things with my bare teeth and hunt in the wild, or live in comfort with a person that loves me? We’ve all probably asked ourselves a similar question—think of any time you've been asked, "What century would you have liked to live in?"
And, unlike most of us—the people who resoundingly answer "21st Century, please! I like clean hospitals with computers!"—Buck opts for the first option.
He wants to answer the call of the wild. He's not playing hard to get:
And not only did he learn by experience, but instincts long dead became alive again. The domesticated generations fell from him. In vague ways he remembered back to the youth of the breed, to the time the wild dogs ranged in packs through the primeval forest and killed their meat as they ran it down. It was no task for him to learn to fight with cut and slash and the quick wolf snap. In this manner had fought forgotten ancestors. They quickened the old life within him, and the old tricks which they had stamped into the heredity of the breed were his tricks. They came to him without effort or discovery, as though they had been his always. And when, on the still cold nights, he pointed his nose at a star and howled long and wolflike, it was his ancestors, dead and dust, pointing nose at star and howling down through the centuries and through him. And his cadences were their cadences, the cadences which voiced their woe and what to them was the meaning of the stiffness, and the cold, and dark. (2.25)
But why? Buck doesn't let the call of the wild go to voicemail because he feels an intense connection to some former, primitive version of himself. London wants us to marvel at Buck’s muscular body and the fact that he can essentially bench press Spitz...but he also wants us to marvel at the untameable nature of Buck's spirit.
His point is that Buck was made to be a wild animal:
Faithfulness and devotion, things born of fire and roof, were his; yet he retained his wildness and wiliness. He was a thing of the wild, come in from the wild to sit by John Thornton's fire, rather than a dog of the soft Southland stamped with the marks of generations of civilization. (6.8)
As they say: you can take the dog out of the primeval forest, but you can't take the primeval forest out of the dog.
But let's talk about strength of bodies a little bit more, because this novel is all about the brawn.
Buck goes through an amazing physical transformation in The Call of the Wild that ends up being a great way to analyze his character arc in the broader sense. Buck's no squirt to begin with; part of the reason he’s stolen from his ranch is that he’s a physically impressive dog. He's ripped:
Perrault grinned. Considering that the price of dogs had been boomed skyward by the unwonted demand, it was not an unfair sum for so fine an animal. The Canadian Government would be no loser, nor would its dispatches travel the slower. Perrault knew dogs, and when he looked at Buck he knew that he was one in a thousand-- "One in ten t'ousand," he commented mentally. (1.45)
But he’s no Rocky yet. He still has to go through a few training montages (Buck's theme song is "Gonna Mush Now") and the transformation process is not all that pleasant. Buck suffers physically in order to gain what ultimately becomes physical dominance. Buck's "glossy coat" gets significantly less glossy, and he ends up run-down, beat-up, torn sideways, and generally deteriorating in every other direction in between.
How does this reflect his character arc in the broader sense? At first, Buck doubts that the wild is the right place for him. And by "doubt" we mean he hates getting beaten with a club and nearly starved to death. (We're pretty sure we'd feel the same way.) This experience corresponds to his physical deterioration— which seems like bad news bears for Buck.
Then he meets Thornton and physically bounces back. (We love you, Thornton.)
But by the time he crosses paths with Thornton, the World's Best Dog Owner, Buck's a changed hound. He finds that he's no longer content to sit by the fire and be man's best friend. The drive that compels him to seek his destiny out in the wilds of the Yukon is almost stronger than his enduring love for his buddy Thornton:
So peremptorily did these shades beckon him, that each day mankind and the claims of mankind slipped farther from him. Deep in the forest a call was sounding, and as often as he heard this call, mysteriously thrilling and luring, he felt compelled to turn his back upon the fire and the beaten earth around it, and to plunge into the forest, and on and on, he knew not where or why; nor did he wonder where or why, the call sounding imperiously, deep in the forest. But as often as he gained the soft unbroken earth and the green shade, the love for John Thornton drew him back to the fire again. (6.11)
In this passage we see the softer side of Buck (he really does heart John Thornton) juxtaposed with the intensity of his desire to become a truly wild doggy. His loyalty to John comes, in part, because Thornton allows him to run a bit wild—Buck's allowed to be the feral beast he is at least part of the time.
But when John is killed, Buck's finally set 100% free. He realizes that the true nature of wildness is to be unburdened, and that freedom really is just another word for nothing left to lose.