Explain why Buck is called the "undisputed master" of Judge Miller's place.

Buck is not the only animal owned by Judge Miller and his family, but he's definitely the most beloved, the most important. The big old hound has the run of Judge Miller's enormous estate. He can go anywhere he likes, exploring the extensive grounds to his canine heart's content. Buck is truly master of all he surveys. None of the other animals have anything like the same degree of freedom: not the fox terriers that live in kennels, and certainly not the pampered house-pets.
Unfortunately, as Buck soon discovers, there's a downside to being such a strong, masterful dog. He becomes an obvious target for unscrupulous men like Manuel, Judge Miller's gardener, who sees Buck's potential as a sled dog in the frozen Klondike. But at the same time, Buck's status as undisputed master of the ranch makes it easier for him to adapt to his new life on the trail. Even before he's kidnapped, he already has more of the wild wolf in him than the other dogs on the ranch, which will stand him in good stead for his subsequent adventures.