Probably the most prototypical sociopath portrayal in literature is Cathy from Steinbeck's East of Eden.
I believe there are monsters born in the world to human parents. Some you can see, misshapen and horrible, with huge heads or tiny bodies; some are born with no arms, no legs, some with three arms, some with tails or mouths in odd places. They are accidents and no one's fault, as used to be thought. Once they were considered the visible punishment for concealed sins.
And just as there are physical monsters, can there not be mental or psychic monsters born? The face and body may be perfect, but if a twisted gene or a malformed egg can produce physical monsters, may not the same process produce a malformed soul?
Monsters are variations from the accepted normal to a greater or a less degree. As a child may be born without an arm, so one may be born without kindness or the potential of conscience. A man who loses his arms in an accident has a great struggle to adjust himself to the lack, but one born without arms suffers only from people who find him strange. Having never had arms, he cannot miss them. Sometimes when we are little we imagine how it would be to have wings, but there is no reason to suppose it is the same feeling birds have. No, to a monster the norm must seem monstrous, since everyone is normal to himself. To the inner monster it must be even more obscure, since he has no visible thing to compare with others. To a man born without conscience, a soul-stricken man must seem ridiculous. To a criminal, honesty is foolish. You must not forget that a monster is only a variation, and that to a monster the norm is monstrous.
It is my belief that Cathy Ames was born with the tendencies, or lack of them, which drove and forced her all of her life. Some balance wheel was misweighed, some gear out of ratio. She was not like other people, never was from birth. And just as a cripple may learn to utilize his lack so that he becomes more effective in a limited field than the uncrippled, so did Cathy, using her difference, make a painful and bewildering stir in her world.
There was a time when a girl like Cathy would have been called possessed by the devil. She would have been exorcised to cast out the evil spirit, and if after many trials that did not work, she would have been burned as a witch for the good of the community. The one thing that may not be forgiven a witch is her ability to distress people, to make them restless and uneasy and even envious.
. . .
Even as a child she had some quality that made people look at her, then look away, then look back at her, troubled at something foreign. Something looked out of her eyes, and was never there when one looked again. She moved quietly and talked little, but she could enter no room without causing everyone to turn toward her.
She made people uneasy but not so that they wanted to go away from her. Men and women wanted to inspect her, to be close to her, to try and find what caused the disturbance she distributed so subtly. And since this had always been so, Cathy did not find it strange.
Cathy was different from other children in many ways, but one thing in particular set her apart. Most children abhor difference. They want to look, talk, dress, and act exactly like all of the others. If the style of dress is an absurdity, it is pain and sorrow to a child not to wear that absurdity. If necklaces of pork chops were accepted, it would be a sad child who could not wear pork chops. And this slavishness to the group normally extends into every game, every practice, social or otherwise. It is a protective coloration children utilize for their safety.
Cathy had none of this. She never conformed in dress or conduct. She wore whatever she wanted to. The result was that quite often other children imitated her.
As she grew older the group, the herd, which is any collection of children, began to sense what adults felt, that there was something foreign about Cathy. After a while only one person at a time associated with her. Groups of boys and girls avoided her as though she carried a nameless danger.
Cathy was a liar, but she did not lie the way most children do. Hers was no daydream lying, when the thing imagined is told and, to make it seem more real, told as real. That is just ordinary deviation from external reality. I think the difference between a lie and a story is that a story utilizes the trappings and appearance of truth for the interest of the listener as well as of the teller. A story has in it neither gain nor loss. But a lie is a device for profit or escape. I suppose if that definition is strictly held to, then a writer of stories is a liar -- if he is financially fortunate.
Cathy's lies were never innocent. Their purpose was to escape punishment, or work, or responsibility, and they were used for profit. Most liars are tripped up either because they forget what they have told or because the lie is suddenly faced with an incontrovertible truth. But Cathy did not forget her lies, and she developed the most effective method of lying. She stayed close enough to the truth so that one could never be sure. She knew two other methods also -- either to interlard her lies with truth or to tell a truth as though it were a lie. If one is accused of a lie and it turns out to be the truth, there is a backlog that will last a long time and protect a number of untruths.
. . .
Nearly everyone in the world has appetites and impulses, trigger emotions, islands of selfishness, lusts just beneath the surface. And most people either hold such things in check or indulge them secretly. Cathy knew not only these impulses in others but how to use them for her own gain.
It is quite possible that she did not believe in any other tendencies in humans, for while she was preternaturally alert in some directions she was completely blind in others.