In the opening of the novel, Buck is owned by Judge Miller and lives a life that could certainly be seen as enviable by any other dog. Buck's life as the judge's dog is pampered, carefree, and devoid of any hardship, and serves as a contrast for the hardship that he will come to endure.

After he is stolen and sold to settle a gambling debt, Buck is briefly owned by a "man with a red sweater," who is not named to symbolize his detachment and cruelty. He mistreats Buck, effectively cowing him.

Soon after he is sold to Francois and Perrault, who are two dispatchers operating in the Yukon region. Under their training, Buck becomes an effective sled dog. This is perhaps the section of the story wherein Buck finds his first true sense of belonging, even becoming lead dog.

Eventually, when they receive different assignments, Francois and Perrault sell Buck to the Scotch half-breed, another vaguely named character who demands an incredibly heavy workload from Buck. The Scotch half-breed works his dogs miserably, to the point that too many of his dogs die to continue.

He sells his remaining three, including Buck, to Mercedes, Charles, and Hal, an inexperienced and ignorant family completely unprepared to face the harsh north. They are abusive to Buck and almost cause his death by demanding that he pull the sled over ice, but Buck is rescued in time by John Thornton, who becomes his owner for life.

Buck's first owner is Judge Miller, who lives in the sunny Santa Clara Valley. Buck enjoys his carefree life on the "sun-kissed" estate, where he rules over the territory and goes on playful hunting trips with Judge Miller's grandchildren. Unfortunately, Buck is stolen by Judge Miller's gardener Manuel, who takes him to Seattle, where Buck is broken by a brutal man in a red sweater. Buck is then sold to two French-Canadians named Francois and Perrault. Francois and Perrault are experienced mail couriers, who drive their sled dogs through the unforgiving Northland. Under Francois and Perrault's care, Buck develops into a skillful sled dog and helps the sled team break records. Both Francois and Perrault are depicted as humane, respectful owners, who value their dogs but push them hard to make deliveries.

In Skaguay, Buck is sold to another mail courier called the Scotch half-breed. Buck suffers under the Scotsman's care and is exhausted from carrying extremely heavy loads. Unlike Francois and Perrault, the Scotsman is not humane and pushes the dogs to their limits. Buck is sold once again to an inexperienced group of owners named Hal, Charles, and Mercedes. They are depicted as ignorant, cruel owners, who exhaust their dogs and place them in compromising, dangerous situations. Fortunately, John Thornton saves Buck from meeting a disastrous fate with Hal, Charles, and Mercedes as they proceed to break through the thin ice.

John Thornton becomes Buck's last owner, and he thrives under his care. John Thornton is portrayed as a loving, sincere master, who truly cares about Buck's well-being. Buck and John Thornton have an amazing relationship founded on love, loyalty, and respect. Buck accompanies John Thornton on many adventures, and John is depicted as the ideal master. Tragically, John Thornton is murdered by a group of Yeehat Indians, and Buck eventually submits to the call of the wild following his death. By the end of the story, Buck runs free in the wilderness with the wolves.

Buck's first owner is Judge Miller.  The offspring of a St. Bernard who had been "the Judge's inseparable companion", Buck lives an idyllic life during his youth on a California ranch (Ch.1).

Buck is then stolen from the Judge by Manuel, one of his ranch hands.  Manuel, in order to pay his gambling debts, sells the dog on the black market to two French-Canadian mail couriers, Perrault and Francois.  Perrault and Francois are humane owners, but make a couple of extremely grueling runs with their team.  After returning from the final run, they sell the team to a Scotch half-breed, who also works the mail.  Buck learns the laws of survival while working on the delivery trails, and eventually vanquishes the lead dog on the team and demands to take his place.

The team is next sold to Hal, Mercedes, and Charles, who plan to use the dogs to take part in the Gold Rush in the Klondike.  The trio is inexperienced and cruel, and eventually meet their demise when they fall into a semi-frozen lake after disregarding warnings that it would be dangerous to proceed upon it.  Buck is saved just before the fatal run by John Thornton, who becomes his final owner.

John Thornton is "the ideal master" (Ch.VI).  Buck serves him with unquestioning devotion until Thornton is killed by Indians.  After Thornton's death, Buck submits competely to the call of his wild ancestors, and leaves the world of man to run with the wolves.