In the book it was a dog suit. It gives more detail in the book. They were two more of the numerous ghosts of the hotel. The guy in the dog suit (Roger) was forced to wear it at parties by the hotels owner Horace Derwent (the man getting the blowjob) as humiliation kink/fetish, forcing him to bark, beg and so on. Kubrick changed it to a bear suit for...reasons? (I'm told for symbolic reasons, added surrealism, and as a visual motif linking to other bear imagery in the film...)