Over the course of three Back to the Future movies, a major plot point that’s never explained is how Marty McFly became friends with Doc Brown. One is a free-wheeling teenager, the other a wild, middle-aged scientist. In reality, they’d probably never even meet, let alone be friends. But from the first frame of film one, we’re forced to buy into this unlikely friendship and we do. And it’s great.

In recent years, though, the series has seen a resurgence thanks to the original’s silver anniversary, non-stop showings on ABC Family and it’s become somewhat fashionable to over analyze the film, including Marty and Doc’s friendship. Under what circumstances did these polar opposites become such good, trusting friends?

Current keeper of the Back to the Future franchise, producer and co-writer Bob Gale, answered that question point blank in a recent interview. After the jump, read the back story he and co-writer/director Robert Zemeckis came up with that never made it into the narrative.

Thanks to Mental Floss (via First Showing) for the quote. Here’s Bob Gale:

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.

That certainly makes sense given the way each character was developed and – fortunately for us – is much less creepy than I’m sure many people surmised.

Are you glad that was left out of the movie? Do you think it would have changed the films in any way if that was revealed?