Angela as we know loves cats. There are various mentions of her cats throughout the series. Mr.Buttface is one of her cats that is only mentioned once or twice before. In the first episode if you listen closly when Dwight is screaming at Jim for putting his stuff in jello again, Angela is talking to Oscar and Kevin. This is where you see her mouth, "My cat Mr.Buttface..." And hence Buttface was born. Not really, he's already a grown cat, but you now what I mean. There is no picture of Mr.Buttface unfortunatly, and Angela never talks about him. So I presume that Angela's cat died before the series started.