This is Fluffy, also known as The Fluff. Dave has never met Fluffy, but the two have very much in common. They could be considered adoptive cousins, as while they are part of the same family, they have no blood relation (presumably). Fluffy, like Dave, is also a big fan of naps, exploring, and eating food. He is also a big fan of the outdoors. Fluffy, however, has much greater access to the outdoors than Dave. As we know, Dave has unfortunately spent little time outdoors since he was 'rescued' from his life on the mean streets of Iowa. Fluffy, meanwhile, lives in a house that is not only much bigger than Dave's, but also has cat-accessible doors, allowing Fluffy to explore the great outdoors whenever he desires.
As you might have noticed in this photograph, Fluffy has something else in common with Dave. Fluffy does not suffer fools gladly.