Answer: Star Wars

Although it might seem as if there have always been movie and franchise themed LEGO building sets, they’re a recent development in the history of the nearly 70 year old toy company.

It wasn’t until 1999 that LEGO began producing sets with franchise themes that deviated from their traditional core theme sets (such as the classic City, Castle, and Space lines). The occasion? The release of Star Wars Episode I: The Phantom Menace. Over a dozen Star Wars themed sets were released around the time of the movie, which were quickly snapped up by Star Wars fans of all ages—a tradition that has been going strong ever since.

Although more themed sets followed, including Harry Potter sets in 2001, Spider-Man sets in 2002 (Studios sub-theme) and 2003 (independent theme), and Batman sets in 2006, the Star Wars themed sets remain the most popular of the movie-themed LEGO sets. In 2016, for example, LEGO announced record profits for the previous year (the net profit for the company that year was a whopping 1.34 billion dollars) and credited the popularity of the Star Wars franchise sets with helping the company continue to grow in the 21st century.