So who is the leader of ''Hell'' in WoW?

If you check the Chronicles Universe structure it has Light, Shadow, Life, Order, Disorder and Death. For Light its the prime Naarus, Shadow the Void Lords, Life Elune, Order Aman'thul and Disorder Sargeras, but for that Death thing we dont know,

http://media.mmo-champion.com/images/news/2016/february/WoWChronicleSample-4.jpg

I dont think its the Lich King because he is just in azeroth and can't represent death in the entire universe , and since when Arthas died he said ''i see only darkness'' and its mentioned that he has gone to ''Hell'' also known as ''The Dark Below'' which is its own realm in the univese so that means that there is a way stronger entity than the lich king that is like the Grim Reaper/Angel of Death. http://wowwiki.wikia.com/wiki/Hell

This also means that we could get another expansion focused on Lich King/Arthas in that Dark Below place redeeming himself and taking the fight to whoever is the leader of the Death realm