The Surprising Novel That Got Kim Stanley Robinson Interested in Science Fiction:
... as a young adult, he checked Clifford D. Simak's comic novel The Goblin Reservation out of the library — and it changed his life.
Honestly, I don't remember mine. I think it may have been the
Tom Swift stories I found at my grandparents' house. I was hooked on Doctor Who the first time I saw a Tom Baker-era episode on Public TV back in the late 70s. No telling which came first though.
Other gateways to geekery?