We are four entities fear us all,
We are the most feared above them all.
Below is our spoken message, prepare your fall,
Mixed and scrambled to watch you fall.
We are all born into this world through blood and pain,
Faced with the inescapable fact that human existence is mad.
Our roles are nothing more than how the times choose to cast us,
But something good always came out of it in the long run.
We got blood in our veins, murder in our eyes, and time on our hands,
It’s easier than explaining what’s killing you inside.
Scars are far more vivid reminders than memories,
As it is, nothing but cold empty contempt.
It’s the inevitable horrid truth of everything:
Everything goes to die.
One bad day to reduce the sanest man,
In suffocation of all that you hold dear.
There are no heroes or villains,
We can choose to be good or bad.
But, I don’t kill humans out of hate. I kill them out of love.
So, I'll slaughter every damn one of you.
Hint:
Three of these villains share the same universe, in a way. Some of them have all met with each other one way or another, but very rarely, and most likely won't for a while. It wasn't for a cup of coffee, that I assure you. The answer is also 100% objective, and there is absolutely no way to argue the objectivity. If your answer feels like a guess, that's probably because it is, and thus, wrong.
Hint #2:
The lines... they're very specific... sources.