Complex sentence: After his death, this weapon was passed onto his protege and successor, Thrall, who, as Warchief of the Horde, has wielded the hammer since then, even up to his retirement as warchief and ascension as a true shaman.
Split into simpler sentences: After his death, this weapon was passed onto his protege and successor, Thrall. Thrall who also succeeded Orgrim as Warchief of the Horde has wielded the hammer since then, even up to his retirement as warchief and ascension as a true shaman.