Introduced as part of the original ("vanilla") WoW, this NPC was simply known as Disciple of Naralex until Patch 4.0.3. He was given the name Muyoh and his original designation changed into his title. Many old-time players were pleased to see his name because we'd spent years wondering just who was Disciple of Naralex.
Wailing Caverns has seen multiple changes since vanilla, changes which also affected Muyoh. Muyoh no longer walks at a snail's pace - like Brann Bronzebeard, he has since learned how to run - and no longer grants Mark of the Wild (a spell deprecated in Cataclysm) when the player speaks to him.
A word of caution to players leveling through the dungeon: Do not allow Muyoh die. He is needed to initiate the final dungeon boss encounter but will not respawn if he dies. If this occurs, the dungeon instance must be reset and completed all over again.
A word of caution to players farming the dungeon: Do not kill monsters too fast while Muyoh is freeing Naralex. The encounter will bug out and Mutanus the Devourer will not appear. If this occurs, the dungeon instance must be reset and completed all over again.