21st Century Nos. 25 & 24: Katy Perry and Ed Sheeran

Our countdown is officially underway with our first two Greatest Pop Stars of the 21st Century: Katy Perry (No. 25) and Ed Sheeran (No. 24)! Billboard's Andrew Unterberger and Jason Lipshutz are joined by longtime KatyKat Joe Lynch to remember the dizzying highs of Perry's early-2010s run, then Sheeran superfan (don't call her a Sheerio!) Walaa Elsiddiq comes on to discuss Ed's unlikely rise from coffeehouses to stadiums. Learn more about your ad choices. Visit megaphone.fm/adchoices