For six months, Dylan was my parents' only cat, and it was clear from the start that he was a very strong alpha male. As he grew older, he became so aggressive that my mom was afraid to even say "No" when he was tearing up furniture. He often scratched her very deliberately and badly.
I had begun to think I would have to find some way to take Dylan home with me just to save Mom from the injuries, but then a friend suggested that getting a second cat might provide Dylan with someone to dominate besides Mom. We went to the shelter and found a fluffy little three-month-old calico girl with a very mellow personality. At the time, we didn't know about proper introduction techniques, so we just put them together and watched closely.
It was amazing: when Dylan set about showing little Sassy who was boss, she drew herself up in the most regal manner, raised one tiny white paw as a warning, and simply stared him down! He never touched her. Later, when she was bigger and stronger, they started tussling as cats do, and even though Dylan weighs 18 pounds now, Sassy can still take him down with her patented Counterclockwise Half-Nelson Whirling Drop... and ten minutes later, the two of them will be entwined in blissful slumber on the sofa.
And Dylan has never laid a claw on anyone since Sassy arrived! In fact, he has become incredibly affectionate toward Mom. Sometimes, he will reach up with both paws, take hold of her wrist, and rub his cheek against the back of her hand. They've been through a lot together, and they're very close now. :-)
So...maybe you need another kitty?