“Indiana Jones and the Kingdom of the Crystal Skull” is based on George Lucas’s story idea. Lucas developed the film’s central concept of moving Indiana Jones into the 1950s, an era associated with flying-saucer films and Cold War science fiction, and using an extraterrestrial crystal skull as the adventure’s mysterious object.
The idea grew partly from an unused crystal-skull storyline considered for The Young Indiana Jones Chronicles. Lucas and Steven Spielberg then shaped the film through several story and script versions. Jeff Nathanson received a story credit with Lucas, while David Koepp wrote the final shooting screenplay, so Lucas was not the film’s sole writer.
A common mix-up is naming Spielberg, who directed the movie, or Koepp, who wrote the final screenplay. The quiz answer points to the originator of the main story concept: Lucas. The film was released in 2008 as the fourth theatrical Indiana Jones adventure, with Harrison Ford returning as Indy after nearly two decades.