Rezh Baphix

The Chorister was a servant of the Mummy of Akhaten. He sang the Long Song along with Merry Gejelh while in the pyramid. The unending song ended with him when the Mummy awoke.

When the Eleventh Doctor and Clara Oswald entered the pyramid to save him and Merry, he teleported from there to save himself. (TV: The Rings of Akhaten)