I don't know exactly what it was, but I just always loved monsters and horror as far back as I can remember. My dad used to rent all the slasher films that were coming out in the early 80s, so I remember many nights sitting as a youngster in the back of our car, being completely fascinated with the VHS boxes as we drove home from the store. I wanted to know everything about Freddy and Jason, and even though I hadn't watched the films, my mind had created enough stories about them to fill up another 30 sequels, haha. The first horror film I saw was NIGHT OF THE LIVING DEAD '68... and the ending shocked me. I loved the zombies, but the bleak conclusion left me honestly disturbed. I was pretty young, haha. After that, I moved through the Universal monster movies (thought, at the time, DRACULA was unbelievably slow-paced, but wound up loving BRIDE OF FRANKENSTEIN), and then moved through the modern classics: HALLOWEEN, NIGHTMARE ON ELM STREET, FRIDAY the 13TH, THE THING, etc.
Haven't looked back since!