Hello. I am a solicitor with over 15 years experience I will try to help you with this. If the original owner gave away or sold the dog to another owner who passed it on similarly to another and then they to another and then that third owner gave you the dog then the dog is yours and the old owner can not claim it back. It is property that has been passed on and belongs to you. The original owner could only claim it back if he is saying that the dog was only lent to someone else who then passed it on without his permission or that the dog was stolen.