Madonna is one of the 25 most important women of the 20th century. It's a big honor mainly coz on that list there are names like Coco Channel, mother Teresa of Calcuta.
See on TIME web magazine

"Every pop star of the last two to three decades has Madonna to thank in some part for his or her success. The triple threat who does it all — chart-topping singer, energetic dancer and all-around provocateur — left her home state of Michigan with $35 in her pocket and a dream to make it in New York City, and far exceeded that goal with hit singles like "Vogue," "Like a Virgin" and "Ray of Light." The one-named wonder's memorable music videos and live performances, which almost always include extravagant dance numbers, over-the-top outfits and eyebrow-raising concepts, made her one of MTV's most popular artists. After causing no shortage of controversy with her unabashed sexuality and outspokenness, Madonna has since turned some of her efforts toward being a mother and humanitarian — but not before cementing her place in pop culture as the best-selling female rock artist of the 20th century."

Source: http://www.time.com/time/