Jack Russell Terrier is a self-assured and loyal dog that takes well to training. While hunting this dog breed is alert and courageous, but at home the Jack Russell Terrier is affectionate and playful. The Jack Russell Terrier is a perky, merry, devoted, and loving dog.  Spirited and obedient, yet absolutely fearless.  Careful and amusing, he enjoys games and playing with toys. The Jack Russell can be aggressive with other dogs if not well trained and socialized.