Once he was freed from Lich King's influence, he sided down with shamans in the seek for truth and knowledge, but they demanded in return the Aurathon, a crystal filled with unknown power to discover. They knew the crystal was cursed, they hoped it kills the Death Knight Morathel, whose blood should purge the crystal from the curse. But he was the worthy one, so Thoron shared his blood and soul with Morathel and made him a sentiel of Aurathon - an elven warrior with dragon-blood and dragon-soul ... I played Skyrim too much :D

As you see, I managed to repaint my Morathel in to Thoron's colour-scheme (I'll upload pic's of them both some later). Was a good training for me since the size of the details like the chains on his gloves or the thin lines on his chest-armor need steady hands and tons of patience ... His eyes was a tricky part too.
In fact, to me he's the best figure in this series, even better than Arthas. Of course, the sculpts on Arthas' armor and sword are much more detailed, but I don't like the shape of it. Additionally, if you compare Sindragosa from Arthas' set with Thoron (Metal Ages Version) by Mega Bloks you'll see who's got a better "pet" ;)