Who is Dennis?!

Now that he has retired, Terry likes to walk to a nearby coffee shop to read. Occasionally he bumps into people he knows.

Not long ago, he was sitting in the coffee shop reading when an attractive young woman sat down across from him.

Are you Dennis? she asked.

No, I'm not, he replied - and didn't give it a second thought.

Several days later, he was again in the coffee shop reading when an older gentleman sitting nearby turned and asked him: Are you Dennis?

No, I'm not Dennis and I've never been called Dennis, Terry replied... But now he's wondering: Who is this person, Dennis... and is he sometimes mistaken for Santa Claus, too?!