The Mad Men finale left us with many questions, but one remains burning in our brains: who wrote the iconic Coca-Cola ad: Don or Peggy? The "I'd Like to Buy the World a Coke" ad campaign was actually written by Bill Backer at McCann-Erickson in 1971, but all Mad Men fans know that the show likes to take a few liberties with the historical time period it's set in. The closing moments of the series finale end on Don, peacefully meditating with a simple smile before fading into the iconic ad.