Sia, her full name being Sia Furler, has been a songwriter for stars for years. She wrote “Pretty Hurts” for Beyoncé as well as “Diamonds” for Rihanna. She saw how those stars lives ended up being because of the public and paparazzi. That was the last thing she wanted for herself. So when David Guetta released their hit “Titanium” with her vocals without telling her, she got noticed.
Right before David Guetta released that song, too, she had decided to retire from recording music herself (which she had been doing since the late '90s). Understandably, she was upset with David Guetta for releasing that without her permission. Sia told NPR that she, “was trying to be a pop songwriter, not an artist”. Given Sia's reputation she acquired from her successful career as a songwriter, she wanted to limit her appearance to the public. That being said, Sia doesn't do tours to promote her own music.
She also tries to hide her face from the press as much as possible. For example, she was on Ellen at one point and when she performed her song “Chandelier”, she stood away from the audience so they only saw her back the whole time. She had Dance Moms star Maddie Ziegler recreate the music video (which if you've ever seen, is just Maddie dancing) while Sia herself stood with her back to everyone. Another time, Sia was on Late Night with Seth Meyers and while she sang (without showing her face to the audience again) one of her friends, Lena Dunham, performed an interpretive dance for everyone. Both Maddie and Lena had on a blonde bob wig, though, which is how Sia is trying to identify herself to the public.
While most artists put their own portraits on their album covers, Sia's album, titled 1000 Forms of Fear, only has a picture on the blonde bob wig. Sia has been quoted saying that she doesn't want to be famous and wants a private life, unlike most stars nowadays.Then again, before her songs blew up and she became known by name for her actual voice, she had done press shots for PETA. She had also been on a few episodes of NBC's The Voice.