Sia may be the busiest "retired" artist in the music business. She's achieved huge commercial success and is famous despite her best efforts not to be. A pop star who doesn't want to be a star, she is iconoclastic, uncompromising, and a little zany. On Twitter, she identifies herself thusly: "i am sia, i was born from the bumhole of a unicorn named steve." In 2013, she agreed to a rare interview with Billboard, but insisted on posing for the cover wearing a paper bag over her head. When RCA Records wanted to sign her, she asked for a clause stipulating that she wouldn't have to tour or do interviews to promote her album. They agreed. She's that good.