Madonna is a legend because she had a huge impact on the pop culture. She started several pop phenomenons. Some of her songs and videos have inspired many generations. See Lady Gaga. She started all these controversies on her music videos and songs before Gaga and Rihanna were born. Every single female pop star will be compared to her. Rihanna, Lady Gaga, Katy Perry, Ke$ha, Britney, Christina, etc. I think only Beyoncé and Alicia Keys don't have real connections to Madonna's work at all. #1 singles aren't what make you a legend. If you ask general people who's currently on the top of the charts, most of them won't have an idea what to say. To become a real legend, you have to start pop phenomenons, have iconic moments and be respected by critcs. Rihanna's last pop phenomenon was "Umbrella". Honestly, she doesn't have memorable performances. And Grammy, VMA, EMA and BET aren't huge fan of hers. Lady Gaga has done more things to become a real legend than Rihanna. Rihanna is just jumping on what's currently hot, working with the toppest producers and doing the most basic made-by-numbers songs. Britney Spears will be a legend. Beyoncé will be a legend. Lady Gaga might be a legend. Rihanna has a lot of work to do. She's just a non-dancer Paula Abdul. Katy Perry has an iconic-ish song, "Firework". But she needs a lot more to become a legend. Ke$ha... Is she relevant?