Sia is a 40-year-old Australian singer and songwriter. Sia always covers her face with a funny mask (面具) on stage. She became famous a few years ago. Before that, she wrote many popular songs for famous singers like Rihanna. Sia had serious depression (抑郁症), but she overcame (克服) it. Her latest album This Is Acting is about her suffering (痛苦的) in life. The song The Greatest shows just how strong and brave Sia is. Go listen to the song and feel the power of Sia.