Back to the Future is one of the most beloved films of the 1980s, but behind its near-perfect facade lies a fascinating mix of behind-the-scenes drama, casting shakeups, scientific inaccuracies, and production quirks that fans continue to uncover decades later.

The film’s journey to becoming a classic was anything but smooth—originally starring Eric Stoltz as Marty McFly, the production was forced to recast after five weeks of filming due to Stoltz’s overly serious tone and method acting, which clashed with the movie’s lighthearted spirit and even created on-set tension with co-star Thomas F. Wilson (Biff). Replacing Stoltz with Michael J. Fox cost $4 million and added serious pressure to the production schedule, but it ultimately paid off, helping the movie gross $385 million worldwide. Casting woes extended to Christopher Lloyd, who initially declined the role of Doc Brown, and Claudia Wells, who stepped away from the sequels for personal reasons, leading to Elizabeth Shue taking over as Jennifer.