It's one of those age-old, universal questions, right up there with: Do aliens exist? Is God a chick or a dude? What happens to the other sock that is lost in the dryer?
Marty and Doc's budding friendship is like a myth, a legend. When Back to the Future begins, the two are already thick as thieves. Did Doc travel back in time to create this collaboration so the adventures in the movie could occur? We thought we'd never know, but now co-creator of the franchise Bob Gale has given the official backstory to the two friends in time.
"Okay, from the horse's mouth (yes, I'm the horse -- er, co-writer, co-creator): We never explained it in the movie. But the history of the characters that Bob Zemeckis and I created is this... For years, Marty was told that Doc Brown was dangerous, a crackpot, a lunatic. So, being a red-blooded American teenage boy, age 13 or 14, he decided to find out just why this guy was so dangerous. Marty snuck into Doc's lab, and was fascinated by all the cool stuff that was there. when Doc found him there, he was delighted to find that Marty thought he was cool and accepted him for what he was. Both of them were the black sheep in their respective environments. Doc gave Marty a part-time job to help with experiments, tend to the lab, tend to the dog, etc. And that's the origin of their relationship. -- Bob Gale"