In the 90s Cher released this song, which is pretty much the dictionary definition of 'pop gamechanger' and also kicked the whole thing off for Brian Higgins and Xenomania (as well as giving Cher herself 'quite a big hit').
Her Twitter account is a fair argument in favour of an artist preserving a little bit of mystique once in a while.
In Summer 2011 Cher announced she had recorded a song with Lady Gaga, which made a lot of people quite excited, but it was just an old rubbish one that Lady Gaga hadn't wanted any more so people got a little bit less excited. By the spring of 2012 the song still hadn't materialised but we have been assured that it exists.