its thrall. I think that was pretty obvious..
[Wowpedia]
After Garrosh's capture, Thrall personally chose Vol'jin to hold the Horde together and pledged his allegiance to him, along with the remaining leaders of the faction. He also resumed his rule over the orcish clans of the Horde and the nation of Durotar.
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except the fact vol'jin sucks when it comes to combat.