4. Harry Potter And The Philosopher's Stone (2001)
Apologies to any American readers out there, but it's not the Sorcerer's Stone. Warner Bros. bought the rights to the book for £1m, which turned out to be a rather shrewd investment seeing as the series went on to spawn eight movies over ten years and become the biggest franchise in history with box-office takings of over $7.7bn. Despite somewhat mixed critical reaction, the opening installment became the second biggest movie in history at the time, with a total gross north of $970m. It may have seemed a gamble at the time to spend $125m on a movie based on a children's book series with three young unknowns in the lead roles but between the rights being purchased in 1997 and the release of the movie, 'Pottermania' took off in a huge way with the first four books available before the first screen adaptation, ensuring a huge fanbase was already in place. Despite the limitations of the main trio, the supporting cast was packed with renowned British actors, with stunning production design and cutting-edge visual effects covering up Chris Columbus' pedestrian direction. As well as kicking off the most successful series of movies ever made, Harry Potter and the Philosopher's Stone also led to studios optioning any fantasy book series they could lay their hands on in the hope of creating a ready-made franchise. In the last decade, dozens of literary adaptations have made their way to the screen in the hope of duplicating the 'Harry Potter effect' with only the Twilight and Hunger Games movies gaining any real traction, countless others having fallen at the first hurdle.