While Back To The Future 4 will never happen, short film Doc Brown Saves The World is the next best thing. Back To The Future is a sci-fi comedy where teenager Marty McFly (Michael J. Fox) accidentally travels 30 years into the past in a time-traveling DeLorean. He must enlist the help of the machine's inventor Doc Brown (Christopher Lloyd) to travel back to his current time while ensuring his parents meet in the past.
Back To The Future is a perfectly formed movie, from casting through to the story. The movie suffered a major bump during production when original lead Eric Stoltz - who had shot on the movie for six weeks - was replaced when director Robert Zemeckis realized he didn't have the comic chops needed. The movie proved to be a huge success and, in a rare move at the time, both sequels were shot back to back. Zemeckis and producer Bob Gale had it written into their contracts there could be no further sequels without their permission, and both have sworn 1990's Back To The Future Part III is the end of the series.
While the series has since spawned cartoons, video games, and theme park rides, Back To The Future 4 still hasn't emerged despite fan interest. While a sequel or reboot is unlikely, fans received some comfort in the form of 2015's Doc Brown Saves The World. This short was created for the 30th anniversary Back To The Future Blu-ray, with Christopher Lloyd reprising his role as Doc.
Doc Brown Saves The World was co-written by Robert Zemeckis and Bob Gale and is set in 2015. Doc records a message for Marty, explaining he's arrived in Hill Valley just before they arrived there in Back To The Future Part II. Doc discovered there was a nuclear holocaust in 2045, which was caused by four specific inventions, including the hoverboard and Mr. Fusion energy reactor. It turns out the invention of hoverboards and hovercars led to the world becoming lazy and obese, which in turn caused giant amounts of trash to accumulate.
Doc Brown goes on to reveal the trash was disposed of by the Mr. Fusion reactors, but a short circuit - caused by Griff Tannen hacking into them in 2045 - caused all their small nuclear reactors to detonate at once. To prevent this, Doc travels in time to erase these inventions. Doc Brown Saves The World is also a response to snarky comments complaining the future of the second film was nothing like the real 2015, with the short explaining that's because Doc erased inventions like self-lacing shoes and hoverboards.
Doc Brown Saves The World ends with Doc declaring his plan a success - only for another Doc to arrive and declare his mission a success too. While there's always a slim hope Back To The Future 4 could happen, it's doubtful it will. For fans of the series, Doc Brown Saves The World is a nice treat and while it's not the same as a full sequel, it's great fun nonetheless.