The 'Harry Potter' film series redefined the modern franchise by keeping the same core cast for eight films over ten years. Starting with 'The Sorcerer's Stone' in 2001, Warner Bros. managed the aging of the child actors (Daniel Radcliffe, Emma Watson, and Rupert Grint) to match the progression of J.K. Rowling’s books. The franchise was remarkably consistent, with every film grossing over $700 million. The final installment, 'The Deathly Hallows – Part 2,' grossed $1.3 billion. This consistency proved that audiences would commit to a decade-long narrative if the quality remained high, paving the way for the later success of the Marvel Cinematic Universe and other multi-film sagas.