We all know Marty thanks to Michael J. Fox, but there was originally a different name attached, Eric Stoltz. The producers wanted Fox originally but went with Stoltz until Fox signed on. They filmed several scenes with the first Marty, including the cafeteria scene where Marty tangles with Biff.
Stoltz did his move wrong and almost broke Wilson’s collarbone – Wilson planned to get revenge by really punching Stoltz at the end of the movie, but couldn’t because Fox replaced him. In addition, Fox does a genuine spit take when he sees Lorraine smoking because he didn’t know there was real alcohol in the bottle he held.
I'm a Nice Guy! Honest!
Thomas F. Wilson plays Biff. The megalomaniac bully. It's by far his most well-known role, and, as it turns out, he's the exact opposite of this violent, mean character. He actually drew upon his real-life high school experiences of being bullied in order to play Biff, who practically turned into the quintessential high school bully.
He wrote a comedic song about how he isn't Biff and has even taken to carrying small laminated cards that have the answers to the most common questions he gets, such as “What is Michael J. Fox like” or “was that real manure.” (Nice, and no.)
Ever wondered why George and Marty eat peanut brittle in "Back to the Future"? Well, the first movie has eight deleted scenes. These include Marty asking a woman to pinch him after he lands in 1955 and a longer “Darth Vader” scene.
There's also a longer scene in 1985 where Marty tries to get George to stand up for himself when a child selling peanut brittle comes to the door. Instead, George crumples like a cheap suit made out of a house of cards, and that, reader, is why George and Marty are enjoying peanut brittle in one scene.
A Hostile Set
One of the reasons Fox was brought in so quickly was because Stoltz was something of a prima donna. Others thought he was too serious for the role, and so when Fox finished his latest project, Stoltz was out and Fox was in.
Neither Tom Wilson nor Crispon Glover got along well with Stoltz, according to them. In addition, Glover proved to be quite more demanding than his character — argumentative, and often battling with director Robert Zemeckis. But, thanks to Stoltz being fired, many of the actors were frightened of doing too much, thinking their jobs might be in danger.
Improvisation Brings the Laughs
In every movie, there will be scenes of ad-libbing or throwing in details that the filmmakers hadn't envisioned, and the "BttF" movies are no exception. Most of George McFly's mannerisms are just Crispin Glover acting naturally or putting his spin on the character, such as his laugh at the episode of "Honeymooners".
He had to try and act “naturally” for the scenes of his improved 1985 self. Huey Lewis actually improvised the line of “I'm afraid you're just too darn loud.”