Harrison Ford might have made it look easy to play a super cool archaeologist adventurer, but if his original script notes are any indication, he actually put a lot of work into Indiana Jones.
The pages below, courtesy of the excellent Tumblr Cinephilia & Beyond, are from Ford's copy of the fifth draft of Lawrence Kasdan's Raiders of the Lost Ark script, dated April 1980. As you can see, he spent quite a bit of time making notes wherever he could, sometimes to revise Jones' lines, sometimes to ask questions about the character, and sometimes just to clarify a point in the story for himself.
Among the more interesting tidbits is the spot on page three where Ford wrote "IS INDY A BELIEVER" in reference to a line where Jones refers to "the power of God." He also notes the moment when Indy realizes "the horror of this situation," when he realizes that the Bible indicates "An army which carries the Ark before it is invincible." Clearly Ford wasn't treating this as just another action movie. He wanted to understand where Indy's academic mind ended and his faith began, which probably means whatever notes he made for Indiana Jones and the Last Crusade are probably just as interesting.
Cinephilia & Beyond also included a documentary about the making of Raiders, which was originally included in the Indiana Jones trilogy DVD set a few years back. If you haven't seen it, it's worth checking out for fun Indy trivia, including some footage of Tom Selleck and Sean Young in audition footage as Indy and Marion.