Why is the Audi A2 considered a pioneer in efficient design?

I've heard a lot about the Audi A2 being one of the most efficient cars on the market, but I'm not sure what makes it stand out. Can someone explain why this car is considered a pioneer in efficient design?

The Audi A2 was designed with lightweight aluminum construction and advanced aerodynamics, allowing for a smaller engine and improved fuel efficiency.

One of the key factors in the Audi A2's efficiency is its use of start-stop technology, which shuts off the engine when the car is stationary, saving on fuel consumption.

Compared to other cars in its class, the Audi A2 has a much lower drag coefficient, which means it has less air resistance and therefore uses less fuel to maintain speed.