This explains it better than I can:
"At a point about three quarters of the way through the novel, when "the hotel was running things," as Jack is about to be served his first drink by the Overlook, Danny walks out of the Torrences' apartment within the hotel and attempts to go to Jack and stop the Bad Thing from happening. Blocking his way, however, is a man "dressed in some sort of silvery, spangled costume. A dog costume...." Danny asks to be let by, but the costumed man begins barking and howling and threatening to "eat [Danny] up," starting with his "plump, little ****." The man then makes references to "blowing down" Harry Derwent, and continues to menace Danny until the boy goes back inside the Torrences' living quarters. Later, during one of those time-bending sequences when the hotel brings its past back to life, the mystery man's identity is explained. One of the Overlook's former owners was a man named Horace Derwent, an eccentric Howard Hughes type who poured over three million into restoring the Overlook after WWII, hoping to make it "the Showplace of the World." At one of his lavish masques thrown for the benefit of the rich and famous, Horace played mockingly with one of the guests - Roger - who was dressed up like a dog. During the hotel's "re-enactment" of the party for Jack, a gorgeous woman explains to him that Derwent is bisexual ("AC/DC...although he never goes for repeats on his DC side"), and Roger is a former lover. According to the woman, Horace told Roger "if he came to the masked ball as a doggy, a cute little doggy, he might reconsider (having sex with Roger)." Although no actual sex scene between Roger, the costumed man, and Derwent is described in the book, Kubrick's vision is a logical extension of their relationship."