We have seen the major Warlords and leaders of the orcs clans from Warcraft 1 and 2, even Durotan
but.. Where is Ogrim Doomhammer?
I have a theory
Garrosh will back in the past and find an Orc called Ogrim, he will try to convince him to join his cause, but after an "accidental death" the original Ogrim, Garrosh will realise that he can "take his place" and put on his armor.
GARROSH will become OGRIM DOOMHAMMER, the former mentor of Thrall, and leader of the Orcish Horde during the last moments of Warcraft 2
The circle... the circle is going to be complete