Michael J. Fox as Marty McFly
Elisabeth Shue as Jennifer Parker
Fun fact: Bob Gale and Robert Zemeckis never intended for there to be sequels to Back to the Future, in fact the ending of the movie was supposed to be open-ended on purpose. In the DVD commentary for the 25th anniversary of the film, Gale said had he known that there was going to be a sequel, he would have never put Jennifer in the time machine too.
Thomas F. Wilson as Biff Tannen
Fun fact: The alternate 1985 storyline where Biff has murdered George McFly was written in because Wilson had signed on to the sequel, and Crispin Glover (who played George) had refused to.
Lea Thompson as Lorraine McFly
Fun fact: Almost all of the costumes for the Enchantment Under the Sea Dance scene had to be recreated since they had been lost, except for Thompson's, who wore the exact same dress for the dance scene in the sequel as she did in the Back to the Future. The reason was because she had taken the costume home and stored it after wrapping the first film.
Flea as Douglas J. Needles
Fun fact: According to Flea, he doesn't really remember filming the scene since he was touring (with the Red Hot Chili Peppers) at the time and flew in just to film his scene in a day, and then leave. He has also only seen the film once, when it was released in 1989.
Christopher Lloyd as Doc Brown
Fun fact: The reason Doc's visit to the rejuvenation clinic was written into the film was so that Lloyd wouldn't have to continue wearing prosthetic makeup to age him like he did in the first film when playing the 1985 version of Doc.