I'm not sure exactly, but I have heard the song is about Zoroaster, the prophet from Freddie Mercury's religion.
I've also heard that it's about a childhood fantasy world that Freddie made up called Rhye (apparently the song My Fairy King is also about this world).
Thank you for your answer(s). My hubby rang me up from work (he's not allowed t'internet) and asked me to Google, but all I came up with were the Queen lyrics.