Elder Torntusk is a level 48 quest giver located on the sacrificial altar at the very top of Jintha'Alor in the contested territory of the Hinterlands.
Be careful if you are Alliance and attempting to obtain the Mallet of Zul'Farrak, Elder Torntusk is a PVP flagged Horde NPC directly on top of the altar you need - but he is not automatically hostile. Attacking him will flag you PvP, but he will not attack you unless you damage him.
He starts the following quests:
[51] Recover the Key!
[51] Return to Primal Torntusk
See List of the Hinterlands NPCs.