Many times a violent animal is often called feral, but this is very incorrect. Other animals, when in their natural habitats, are not inherently violent without good cause.
Other animals are driven by the same needs we have; food, shelter, and social structure. When these are lacking any animal becomes antisocial, and even violent, in their pursuit to get their needs met.
Cats are the best example, every time I see a cat called feral it has always been given this label due to antisocial behaviors. The reasons for these behaviors have always been correctable, usually with basic medical care.
Antisocial behavior toward humans is expected if the cat has been abused, their natural social structure allows for it but does not encourage it. A feline society is loosely hierarchical, the alpha watches over the pride in exchange for a few privileges.
If the alpha feline ever fails to protect the pride, or abuses their position, then the other members rebel. A natural reaction, even among humans.
If the alpha is a different species, then trust must be earned again. This is often why many felines will become violent toward humans, they have been abused or neglected by the human they once respected as the alpha.
So taming them is simply not a solution, actually we never tamed any of the other animals, ever. Even if they obey out of fear, they are still willing to rebel once the opportunity presents itself.
This is what violent cats and dogs are doing, rebelling. They learned that by acting violent they will be sent away, even if left in solitude they prefer the shelter to human interaction.
To alter this behavior there is one simple thing that they need to see, you need to love them, and you need to love them a lot. First, ignore all their outbursts as much as possible.
This means you will be hurt, but if you love something you will be willing to go through this just to save their life. Only offer them affection when they are calm and loving, eventually they'll expect the reciprocation.
Learn what they want, and give it to them; a few exceptions to this exist, cats can't have too much tuna so only give them that in small amounts. Usually the things they want are actually quite convenient, like playtime or a specific kind of toy.
Cats have sensitive spots that most other animals do not, for this reason you have to learn how to pet them correctly. The catch is that it varies for each cat.
Very few cats like to be petted near their tail, so that may be a trigger. It could also indicate a medical issue if they respond with ferocity, so you may want to have that checked out.
Most cats will guide you, just put your hand out and watch what they rub up against you, that's where they want to be petted. The more they trust you, the more contact they will tolerate.
No one likes to be touched, grabbed, or petted by someone they do not trust, the same is true of cats. A violent cat will likely not want to be petted until they are certain you will not harm them.
Patience is key here, you adopted them for love but they learned to fear instead. So you have to teach them what love actually is, and show them that you also want to be loved.
I have dealt with many violent cats, and several actually feral ones, and I have always been able to earn their trust. In doing so, you will find that they are the most grateful felines.