who replaced him?
Jeffrey Weissman.
Back to the Future Part II
Rather than write George out of the film, Zemeckis used previously filmed footage of Glover from the first film as well as new footage of actor Jeffrey Weissman, who wore prosthetics including a false chin, nose, and cheekbones to resemble Glover. 
who played marty in back to the future Michael J. Fox what was the premise of the film? Marty McFly, a teenager accidentally sent back in time to 1955 in a time-traveling DeLorean automobile built by his eccentric scientist friend Doctor Emmett "Doc" Brown. what kind of cultural impact did the film have? "Back to the Future" has influenced or been referenced in a variety of media, including: "American Dad". does it have any sequels? Yes, "Back to the Future Part II". does it have same character mentioned above? Yes. was it played by same actor? Yes. were any actors from the first film replaced while making the sequel? Yes, Crispin Glover.
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Back to the Future Part II [SEP] Replacement of Crispin Glover
Rather than write George out of the film, Zemeckis used previously filmed footage of Glover from the first film as well as new footage of actor Jeffrey Weissman, who wore prosthetics including a false chin, nose, and cheekbones to resemble Glover. Various techniques were used to obfuscate the Weissman footage, such as placing him in the background rather than the foreground, having him wear sunglasses, and hanging him upside down. Glover filed a lawsuit against the producers of the film on the grounds that they neither owned his likeness nor had permission to use it. As a result of the suit, there are now clauses in the Screen Actors Guild collective bargaining agreements stating that producers and actors are not allowed to use such methods to reproduce the likeness of other actors.