Ever wonder how Marty McFly and Doc Brown met and became friends pre-Back to the Future.
Well, series co-writer Bob Gale has filled in the blanks. Here’s his official explanation of how the two met and forged a friendship.
“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,” he says. “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.”
It doesn't hurt that the Doc had already met Marty years before Marty was born. Pre-destination paradox and all that.
Yeah, Doc knew he would eventually meet Marty, so when they run into each other that first time, he knew what type of person Marty was going to be. Doc may have even gone out of his way to keep Marty around, so that they were able to become friends.
Except Gale is talking about original-timeline Marty and Doc, meeting before they had an earlier history. Now, presumably, Marty still remembers that original meeting but Doc remembers an alternate "meeting" at which he already knew Marty from 1955 and had to pretend he didn't. /pedantic mode