MacGuffin

The MacGuffin is a plot device in fiction that drives the action forward. Within the films of Indiana Jones, this typically refers to the object that the titular archaeologist is searching for.

Although franchise creator George Lucas conceived of Indiana Jones as an archaeologist who sought out supernatural artifacts, it was Philip Kaufman who came up with using the Ark of the Covenant for Raiders of the Lost Ark, influenced by an old dentist of his who was "obsessed" with the powers of the Ark.

For Lucas, the Ark was the perfect MacGuffin, but struggled to conceptualize suitable follow-ups on his own for the subsequent three sequels.

He raised the idea of using the Holy Grail for what developed into Indiana Jones and the Temple of Doom but director Steven Spielberg pushed against it, feeling that the MacGuffin was not strong enough. Eventually the production settled on the Sankara Stones but Lucas would ultimately look back on them as having been too esoteric.

The Holy Grail was revisited for Indiana Jones and the Last Crusade. As Spielberg wanted to explore Indiana Jones' relationship with his estranged father, Henry Jones, Sr., he used Indy's search for the Grail as a metaphor for the search for Henry Jones.