Biggie observed that the other two cats were not bothered by the dog and they would rub up against her and sleep by her. It was like the dog was their protector. Gradually, Biggie came closer to Riley, without ever touching her. All of the animals seemed to get along and there was peace in the home.
All of a sudden, one day Biggie came face to face with Riley and went beserk. He hissed and arched his back violently. He growled menacingly and started for Riley with both front claws extended, ready to attack the dog. My wife, who was standing nearby in the kitchen intervened, scolded the cat and tried to separate the two animals. When she did this, Biggie swatted her with his claws and wounded her on one of her hands and arm. He then turned and ran away into another room to hide.
This became the new norm. If Biggie came into the living room, where all of the animals congregated during the day and he spotted Riley, he would go into attack mode and charge Riley, resulting in more human intervention and more scratches on the arms.
This aggressive behavior went on for about a month. We tried squirting water at Biggie, but it only made him mad and he continued to attack Riley. We didn’t know what to do.