Who played Scarlett O’Hara in 1939’s Gone With the Wind?

Before there were the Kardashians, there was Gone With the Wind. The 1939 epic drama was essentially a reality show wrapped up in Civil War-era rich people having parties.
And Scarlet O’Hara seems to have no problem being front and center in all the drama. She’s a driving force of the film, and casting her was notoriously difficult — it’s said that over 1,400 women were interviewed for the part.
But only one person could do Scarlett justice, and she did it really damn well. But who was it?