In 1978, George Lucas, Steven Spielberg, and Lawrence Kasdan had early brainstorming sessions around Lucas's outline for "Raiders of the Lost Ark." They recorded the conversations and had the tape transcribed. Here it is (PDF). Over at the New Yorker, Patrick Radden Keefe provides a summary and excerpts some choice bits.
The hero, Lucas explains, is a globe-trotting archaeologist, “a bounty hunter of antiquities.” He’s a professor, a Ph.D.—“People call him doctor.” But he’s a little “rough and tumble.” As the men hash out the Jones iconography, they refer, incessantly, to other films, invoking Eastwood, Bond, and Mifune. He will dress like Bogart in “The Treasure of the Sierra Madre,” Lucas says: “the khaki pants…the leather jacket. That sort of felt hat.” Oh, and also? “A bullwhip.” He’ll carry it “rolled up,” Lucas continues. “Like a snake that’s coiled up behind him.”"Raiders of the Lost Ark: Story Conference Transcript" (Mad Dog Movies)
“I like that,” Spielberg says. “The doctor with the bullwhip.”
"Spitballing Indy" (The New Yorker)