Acting for Two: Michael J. Fox plays Marty, his older self in 2015, his children Marty Jr. and Marlene (yes, the daughter), and Seamus in 1885.
Christopher Lloyd shares a scene in Part II with himself as Doc meets his 1955 self.
Thomas F. Wilson plays 1955 Biff Tannen, 1985 Biff (three versions, no less: the Jerk Ass from the beginning of Part I, the wimpy version from the end of parts I and III and beginning of Part II, and the Jerk Ass In Chief from the 1985-A universe in Part II), 2015 Biff and his grandson Griff, and Buford "Mad-Dog" Tannen in 1885.
Lea Thompson portrays both Lorraine Baines-McFly, George's wife, in 1955, three versions of 1985, and 2015, and Maggie McFly, Seamus's wife.
Elisabeth Shue plays Jennifer's younger and older self at the same time in Part II.
Dawson Casting: Marty, Lorraine, George, Biff, Jennifer, etc. Makes some sense in Lorraine, George, and Biff's cases, since in the first movie they had to play both their teenage selves and their adult selves. Initially, not so much the case with Jennifer, who was played by 19-year old Claudia Wells in the first film, but then played by 26-year old Elizabeth Shue in the Sequels and that wig she wore to make her resemble Lea Thompson made her look every bit her age.
Defictionalization: DeLoreans built nowadays include a Flux Capacitor in the back seats (though, of course, it's just for show).
There are no back seats in a DeLorean, original or newly built; they only have a pair of front bucket seats. (That's why Jennifer had to ride sitting in Marty's lap.)
Disowned Adaptation: Bob Gale hated many of the video game adaptations of the franchise, particularly the first one by LJN Toys. According to him, the makers of the game didn't want any input from the filmmakers, and when he saw it, he wanted a lot changed, but was told it was too late to do anything. He advised fans not to buy it, and felt that Telltale Games handled the process much better.
Executive Meddling: Basically, this is the whole reason why the sequels exist in the first place — but Sid Sheinberg had insisted on certain changes to be made in the first movie.
One of Sid Sheinberg's changes, from "Professor Brown" to "Doc Brown", has become integral in Back to the Future culture. (Just how much so is suggested by Michael J. Fox's repeated bloopers in filming The Frighteners: he called the Judge character "Doc".) He also insisted on Emmett Brown's chimpanzee pet being changednote his reasoning was that movies with chimps didn't make money; when the Eastwood Any Which Way films were pointed out, he retorted "That was an orangutang.", which became the dog Einstein, and requested Marty's mother's name go from Meg to Lorraine (his wife's name). The last note is mentioned in the first film's trivia in regards to the title, to which the Bobs adamantly stuck to their guns.
Cost considerations forced a complete change in the tactic to return to 1985 in Part I, from powered by a nuclear test explosion to powered by the lightning bolt. By all accounts, it was a major improvement, as keeping it "local" in Hill Valley added an immediate urgency and gave Doc something to do with the clock tower (in the original script, he simply watched from a mountainside).
He also started carrying small laminated cards he'd hand out to fans he'd run into, featuring answers to the most frequent questions he's asked about the movies.
Fake American: Marty McFly — Michael J. Fox is in fact Canadian. You can hear his accent slip when he pronounces "sorry" as "so-ree."
Hey, It's That Place!: Courthouse Square, on the Universal Backlot, has been in dozens of productions. The set tragically burned to the ground in 2008. It has been rebuilt however.
Mean Character, Nice Actor: The actor of Biff Tannen, Thomas F. Wilson, is a painter and a comedian, very approachable to fans and likes to joke about the questions he's getting regarding his role as Biff. He's also Happily Married with four children. Word of God also vouch for this in various commentaries and Q&As. Not only is he not a bully in real life, he drew on his real life experiences of BEING bullied in high school to play Biff. And he really doesn't like it when fans ask him to call someone a butthead.
There are three Joeys in the trilogy: Marty's uncle "Jailbird" Joey, one of Biff's goons (nicknamed "Skinhead"), and the barkeep's assistant in 1885.
The Other Darrin: Elisabeth Shue replaced Claudia Wells as Jennifer Parker in the sequels. Likewise, Jeffrey Weissman replaced Crispin Glover as George McFly.
The Red Stapler: The DeLorean. At the time the movie came out the Delorean Motor Company had been bankrupt for almost 3 years and DeLoreans were considered a failed car. Nowadays there's an active "time machine conversion" community, DeLorean dealers, and DeLorean conventions — all because of Back to the Future. There's apparently even a company in Texas that bought the rights to the design and is making new DeLoreans.
Scully Box: Because Christopher Lloyd is 6'1", much taller than the 5'4" Michael J. Fox, camera tricks were used to avoid using one. For example, the two are rarely in the same shot together and, when they are, one is usually sitting down or much closer to the camera than the other. When Doc Brown is talking, he's often moving around so much that the viewer can't really tell how tall he is. Lloyd also improvised a hunch in his posture that helped give the character more of a Mad Scientist look.
Unintentional Period Piece: The 1985 scenes, by being so current at the time of filming, falls headlong into this. Justified, in that the differences in eras wouldn't be nearly as significant if they'd been downplayed.
Urban Legend of Zelda: Once real-life history got into the decade of the 2010s, pretty much every year there would be a picture claiming that that day was the day Marty went to when he went to the future (with the date being photoshopped to the current date). It's easy to tell the fakes, since the real years in the movies all end in 5. Now that the real date has passed, only time will tell if these fakes will stop being made.
Big Name Fan: When the film was screened at the White House, Ronald Reagan personally asked the projectionist to rewind the film to Doc's disbelief about "the actor" who became president. Not only did he find the line hystericall, but he would use the line "Where we're going, we don't need roads" in his following state of the union address and was even offered a part in the third film.
The Cast Showoff: Kind of. Although Michael J. Fox is miming his performance of "Johnny B. Goode" he did actually learn to play the song (having played guitar in high school) so he could do so accurately.
Wonder why George had peanut brittle for dinner in 1985? Originally, after meeting with Biff, Marty tries to urge George to stand up for himself when a child selling peanut brittle shows up. Instead, he caves, buying all of it, with the child's father saying "See, I told you we'd only have to stop at one house."
The 1955 Doc looks at the contents of his 1985 counterpart's suitcase, which include a Playboy magazine and the hair dryer Marty takes with him while playing "Darth Vader".
In 1955, before Doc gets introduced to George, Doc and Marty see Lorraine cheating on a quiz in class, surprising Marty.
The Darth Vader scene was longer, with more sci-fi references, such as Marty telling George "You are entering The Outer Limits of The Twilight Zone!", ending with Marty knocking George out with chloroform, explaining how George overslept and missed school. It got cut because it lasted too long and was redundant.
The whole scene can be found on Blu-ray and DVD releases, as well as here.
Just when Marty leaves for the dance, Doc gets asked for a permit for his "weather experiment", and Doc gets it: a $50 bill, quite a bit of money back then. Also, Marty worries about his plan, asking "What if I go back to the future and I'm gay?", to which Doc says "Why shouldn't you be happy?"
George, realizing he's late during the dance, goes into a phone booth to confirm the time, but Dixon, the bully who'd kicked George and later cuts in on him and Lorraine, traps him inside, with Strickland chastising him.
Enforced Method Acting: Two examples that didn't make the film because of Eric Stoltz. When they filmed the cafeteria scene, Stoltz roughed up Thomas F. Wilson for real and Wilson almost broke his collarbone. The normally nice guy Wilson planned to get revenge during the car park scene at the dance by actually punching Stoltz but Stoltz was fired by then so he never got the chance.
Executive Meddling: Attempted, but thwarted by the power of Spielberg. Universal head Sid Sheinberg didn't like the title Back To The Future and sent Spielberg a memo suggesting that it be changed to Spaceman From Pluto, in reference to the two scenes in which Marty is mistaken for an alien while in his hazmat suit, and asked that those two scenes be re-written to accommodate the title. Spielberg, who was good friends with Sheinberg and wanted to let him down gently, sent a letter back thanking him for "the wonderful joke," and Sheinberg was too embarrassed to admit he was serious.
Foreshadowing: If one is fast enough, you can see Future-Doc (with the hat and bike) from Part II, leaving the town square as Doc is setting up the "specialized weather-sensing equipment."
Word of God is that it was coincidental — just a random detail added to the scene. Also, Doc departs in the opposite direction in Part II.
Non-Singing Voice: Michael J. Fox did not sing "Johnny B. Goode", although he did learn to play it so he could "mime" the guitar.
The Other Marty: The Trope Namer. Eric Stoltz was cast as Marty, and filmed some scenes, before being replaced by Michael J. Fox because people felt Stoltz was too serious for the role. You'll get to see some Stoltz footage in the Blu-Ray release of the Back to the Future trilogy.
Throw It In: Many of George McFly's mannerisms (the shaking hands, the infamous Honeymooner's laugh) were ad libbed by Crispin Glover. Allegedly, much of that was Glover's normal behavior, and the real challenge was getting him to act normal for the improved-1985 scenes.
Huey Lewis improvised the line "I'm afraid you're just too darn loud", as the silly excuse for Marty's band to be rejected.
During the "Mister Sandman" Sequence, when Marty sees the 1955 Texaco gas station, there was originally only one attendant working on a car, but Robert Zemeckis had the costume department find 3 more attendant costumes, believing it'd be funnier.
According to Bob Gale, Red (the homeless guy)'s name was ad-libbed by Michael J. Fox.
Troubled Production: Everyone involved in the first film was sure it would bomb because absolutely nothing went smoothly. (Among the crew, it was nicknamed The Film That Would Not Wrap.) The shoot nearly drove Zemeckis insane, ruined his health, and threatened to wreck his career if the film wasn't a hit. Star Michael J. Fox was running on fumes, commuting between the BttF and Family Ties sets with virtually no sleep in-between. In his interview on Inside the Actor's Studio, he notes that he was basically a zombie, which luckily enhanced his acting a fair bit.
The Bobs (Zemeckis and Gale) originally pitched the idea to Disney and then Columbia, both of whom turned it down due to problems with the "kid dating his young mother" part of the story, albeit for completely opposite reasons: Disney felt that it was too raunchy, Columbia didn't think it was raunchy enough!
The original time machine was a modified refrigerator, changed because it would have been a very stationary prop and Steven Spielberg had images of children locking themselves in the fridge to the horror of their parents. They also would have driven into the blast of a nuclear bomb to fuel the flux capacitor, changed because that alone would have doubled the production costs and the clock tower lightning strike made a fairly simple and stationary location. In the script written for this kind of time machine, the original timeline's Biff became a cop that kept "borrowing" stuff from George and had a daughter. With the change in the timeline, Biff became a security guard working for George, who became a boxing champion in that script.
For younger readers who don't understand how someone could become trapped in a refrigerator, they used to be held closed with a physical catch that could only be opened by a handle on the outside, and these older models were still somewhat plentiful at the time of the film. Modern ones all use magnets to hold themselves closed, with no catches.
Eric Stoltz was originally cast as Marty; apparently only stills and a few clips exist of his work on the movie except for one scene that made it into the final cut — Stoltz running away from the terrorist van, entirely covered in a radiation suit. When initially casting Marty, the producers narrowed it down to two choices: Stoltz and C. Thomas Howell. Michael J. Fox was always their first choice, but the producer of Family Ties initially didn't want Fox gone from the show during Meredith Baxter's pregnancy. Zemeckis and Gale preferred Howell, but the executives preferred Stoltz, so Stoltz was cast. However, the execs told the Bobs that if Stoltz didn't work out, then they could go back and reshoot with another actor. Except no-one expected it to actually happen...
The situation with Stoltz also affected the casting decisions of two other characters:
Melora Hardin (who would later play Jan on The Office (US)) was originally cast as Jennifer to play opposite Eric Stoltz's Marty. However, Melora never filmed any scenes, and was fired after Marty was recast because she was a lot taller than Michael J. Fox, which actually alienated many of the female crew members, while the male crew members had no problem with it, whatsoever.
J.J. Cohen was considered for Biff, but he was cast as Skinhead instead due to the fact he wouldn't have looked physically imposing next to Stoltz. Bob Gale has said that had Michael J. Fox, who Cohen is taller than, been cast from the beginning, Cohen probably would've won the role.
Also, John Lithgow was considered for the part of Doc Brown. In fact, Lloyd was ready to pass on the film, but his wife insisted the script was better than it looked.
Jeff Goldblum was another consideration for the role of Doc Brown.
The producers considered using "Papa Loves Mambo" by Perry Como when Marty arrives in the 1955 Hill Valley, before deciding on "Mister Sandman", thereby making it the "Mister Sandman" Sequence. "Papa Loves Mambo" would however show up in Part II where it's the song playing on the car radio as Biff drives to the dance.
Channel Hop: More than a decade after the original run on CBS, the show resurfaced from March to August 2003 on Fox on their then-new "Fox Box" Saturday morning lineup, programmed by 4Kids Entertainment- likely to fill the E/I quota.
Keep Circulating the Tapes: Only 18 episodes made it to VHS and Laserdisc, and none of them made it to DVD until October 20, 2015, when Universal released a Complete Series DVD set of the show—one day shy of the "futuristic" date Marty, Doc, and Jennifer visited in BTTF Part II. Up until then, you had the aforementioned incomplete releases, and whatever tapes were circulating from the original run on CBS, and the reruns on Fox (see above).
Actor Allusion: In Episode 3, Marty's brother, David, is said to be working for a newspaper in a big city and his sister, Linda, is said to be in a womens' boarding house. Marc McClure played Marty's brother in the movies, and also played Jimmy Olsen in Superman. Wendie Jo Sperber co-starred in Bosom Buddies, set in an woman-only hotel. As an added bonus, both actors played these roles before the first movie came out.
Young Emmett says his flying car idea will make traffic jams a thing of the past, which is the same thing Judge Doom - another character played by Christopher Lloyd - said about his freeway idea.
It turns out Trixie Trotter is Canadian and Marty's grandmother. Michael J. Fox is Canadian.
Development Gag: Not a gag relating to the development of the game, but to Back to the Future Part III. In Episode 1, Marty can find an old photograph of Marshall Strickland in Edna Strickland's home. Edna states that he had been shot and killed by Buford Tannen. Marty (who, of course, had been to 1885 when Strickland was alive and who was instrumental in Buford being sent to prison) states that he doesn't remember that occurrence. While there's an in-story reason for this (he wasn't there when it happened nor informed of the events), the joke is actually a meta-joke about how the scene depicting Strickland's death was cut from the film.
Episode 1 references a gag from the aborted Number Two script, wherein Marty is arrested, and chooses the alias "Marty DeLorean" to get Doc's attention through the newspapers. In the video game, however, it's the other way around: Doc is arrested, and chooses the alias "Carl Sagan" to get Marty's attention through the newspapers.
In Episode 3, George has a box of peanut brittle on his desk by the monitors. This refers to a deleted scene in the original Back To the Future where George displays what a wimp he is by being bullied into buying tons of peanut brittle. The only remnant of this in the final film is a shot of him pouring some into a bowl.
Orphaned Reference: The names of Marty's grandparents are lifted from early versions of the script for the original film and the novelization.
Talking to Himself: AJ LoCascio plays both Marty and Alt-1986!Jennifer's scumbag boyfriend in Episode 3.
George's reluctance at letting Robert Zemeckis adapt A Match Made in Space into a movie references an article in USA Today's Real Life reproduction of the 2015 newspaper cover prop. According to this page, the phony article was written by Gannett vice president Matt Urbanos to replace the junk filler used by the original newspaper prop.
One popular fan theory was that Doc reverse engineered the hoverboard in order to get the time train working, since the board was pretty much the only bit of future tech at his disposal at the time. This idea was sort of used in "Continuum Conundrum," when Doc mentions he used components from the hoverboard to help get the steam trike time machine working.