The very earliest?
Grimm's Fairy Tales and Bullfinch's Mythology

The fairytale I studied over and over again was about two sisters Rose Red and Snow White. Not the two who befriend a bear but two who ahave magic powers and are chased by a witch with seven league boots (she lived under my bed and I still sometimes dread to put my feet on the floor at night). The problem I always had with it was if the sisters had enough magic power to turn themselves into roses, how could they have not had enough sense to choose the same color. Thewitch sees one white rose on a bush of red roses and plucks it knowing she has caught at least one of them.

Greek mythology (I snuck the unopened book from a friend's house) was a secret place all my own. No one else was interested. I had Jason and Medea, Hercules, centaurs, minotaurs, Medusa, Pegasus, etc. all to myself. And gradually I started to see relationships between my own religion and mythology. By the age of ten I had decided to learn Latin and Greek and study Classical literature.
I also found that same theme of forgetfulness, foolishness, whatever, bringing down hero after hero. Theseus "forgets" Ariadne and leaves her deserted on an island. Oedipus, who has been told that he will kill his father and marry his mother, "forgets" and marries a woman old enough to be his mother after accidentally killing her husband. DOH! Pandora, warned not to open the box, does anyway. And why is "HOPE" the only thing left in a box of evils? Is HOPE the ultimate evil. Fatal flaws, hubris, family relationships, mores,...

I was always told "You think too much". But I never regretted getting sucked into that particular line of thought.

Later? Ayn Rand. Robertson Davies. Clive Cussler. Jane Austin. Trollope. Faulkner. Sir Richard Burton. The Bronte Sisters. And any piece of horror trash I can get my hands on though Steven King bores me to tears except for The Shining - book not movie.