What was the most important thing Leonardo da vinci ever did?

Leonardo was the first painter to examine the human body in great detail by dissecting cadavers. (Dead people) His sketch called Vitruvian Man is considered a masterpiece of human musculature, even today. He went on to invent a method of painting using lighting from the rear, for instance, that created the first paintings of humans almost jump off the canvas, such was the reality. This led to the modern system of painting.