With four doors, an electric powertrain, and available all-wheel drive, the 2021 Mustang Mach-E takes one of Ford's most storied nameplates into uncharted territory. While building an electric Mustang is a relatively new idea, the pantheon of automotive history is full of design studies that explored how to make the world's most popular pony car more family-friendly. Ford experimented with two-seater models early on, and it transformed a coupe into a four-door sedan in 1963.