Who is the mysterious person behind the glass?

An old, tired-looking dog wandered into the yard. I could tell from his collar and well-fed belly that he had a home.
He followed me into the house, down the hall, and fell asleep on the couch. An hour later, he went to the door, and I let him out. The next day he was back, resumed his position on the couch and slept for an hour. This continued for several weeks. Curious, I pinned a note to his collar: "Every afternoon your dog comes to my house for a nap."
The next day he arrived with a different note pinned to his collar: "He lives in a home with four children -- he's trying to catch up on his sleep. Can I come with him tomorrow?"