My nickname for him is little one. It's funny you should say that because my daughter has made up a voice for him and he is constantly saying, "NOT LITTLE!" Little dog- BIG attitude.
Here is an interesting point of fact: the Jack Russell Terrier (Not to be confused with the Parson Russell Terrier or the Russell Terrier) is not recognized by the AKC (American Kennel Club) because the JRTCA (Jack Russell Terrier Club of America) wanted to protect their heritage as a working dog. What invariably happens to breeds that become AKC recognized is that they lose the characteristics for which they were originally bred. Fortunately Max my Rhodesian Ridgeback has not lost his characteristics. Ever since I've had him I haven't seen the first lion in my yard.