Well, Buck, my boy, we've had our little ruction, and the best thing we can do is to let it go at that. You've learned your place, and I know mine. Be a good dog and all will go well and the goose hang high. Be a bad dog, and I'll whale the stuffing outa you. Understand?
~ The Man in the Red Sweater to Buck.
The Man in the Red Sweater is a major character in Jack London's 1903 short adventure novel The Call of the Wild. He is a dog-breaker who tries to teach Buck the law of the club. He does not beat dogs out of cruelty, rather he looks to teach these dogs the lessons that will allow them to survive in this harsh environment.
When the smugglers gingerly carried Buck's crate from the wagon into a small, high-walled back yard, the man in the red sweater that sagged generously at the neck, came out and signed the book for the driver. That was the man, Buck divined, the next tormentor, and he hurled himself savagely against the bars. The man smiled grimly, and brought a hatchet and a club. Buck rushed at the splintering wood, sinking his teeth into it, surging and wrestling with it. Wherever the hatchet fell on the outside, he was there on the inside, snarling and growling, as furiously anxious to get out as the man in the red sweater was calmly intent on getting him out. Straight at the man he launched his 140 pounds of fury, surcharged with the pent passion of two days and nights. In mid-air, just as his jaws were about to close on the man, he received a shock that checked his body and brought his teeth together with an agonizing clip. He whirled over, fetching the ground on his back and side. He had never been struck by a club in his life, and did not understand. With a snarl that was part bark and more scream he was again on his feet and launched into the air. And again the shock came and he was brought crushingly to the ground. This time he was aware that it was the club, but His madness knew no caution. A dozen times he charged, and as often the club broke the charge and smashed him down.
After a particularly fierce blow he crawled to his feet, too dazed to rush. He staggered limply about, the blood flowing from nose and mouth and ears, his beautiful coat sprayed and flecked with bloody slaver. Then the man advanced and deliberately dealt him a frightful blow on the nose. All the pain he had endured was nothing compared with the exquisite agony of this. With a roar that was almost lion-like in its ferocity, he again hurled himself at the man. But the man, shifting the club from right to left, cooly caught him by the under jaw, at the same time wrenching downward and backward. Buck described a complete circle in the air, and half of another, then crashed to the ground on his head and chest. For the last time he rushed and the man struck the shrewd blow he had purposely withheld for so long, and Buck crumpled up and went down, knocked utterly senseless. He then threatens Buck to be friends with him or he'll continue to beat him.
Buck was beaten (he knew that); but he was not broken. He saw, once for all, that he stood no chance against a man with a club. He had learned the lesson, and in all his afterlife he never forgot it. That club was a revelation. It was his introduction to the reign of primitive law, and he met the introduction halfway. The facts of life took on a fiercer aspect; and while he faced that aspect uncowed, he faced it with all the latent cunning of his nature aroused. As the days went by, other dogs came, in crates and at the ends of ropes, some docilely, and some raging and roaring as he had come; and, one and all, he watched them pass under the dominion of the man in the red sweater. Again and again, as he looked at each brutal performance, the lesson was driven home to Buck: a man with a club was a lawgiver, a master to be obeyed, though not necessarily conciliated. Of this last Buck was never guilty, though he did see beaten dogs that fawned upon the man, and wagged their tails, and licked his hand. Also he saw one dog, that would neither conciliate nor obey, finally killed in the struggle for mastery.
A few days later, a pair of French Canadians named Francois and Perrault came and bought Buck and Curly and the man isn't seen again for the rest of the story.
He is called "Digger" in the 1976 film. Whether that's his name, his surname or a nickname of his isn't mentioned.
His name is Bob in the 1981 anime film Call of the Wild: Howl Buck.