Board Thread:Lore Discussion/@comment-11296535-20130914180002/@comment-6941549-20130914180459

It is not explained. normally dragons are amortal and can only be killed if the dragonborn devores or absorbs it soul. So I think that Numinex killed himself by transferring his soul to King Olaf One Eye.

you may go really Alduin. But Numinex went crazy and even forgot his own name. If that happened to me I would want to die, just so I did not have to go through the anguish any more