Corporal Thund Splithoof is a level 55 quest giver located by the entrance to the Blasted Lands in the contested territory of Swamp of Sorrows. He is only visible once you complete the Fallen Hero of the Horde's quest "The Stone that Binds Us".
The Fallen Hero redirects you to Thund who gives you a chest with the inside. There is a specific demand you trigger with the Fallen Hero of Horde to "summon" him, directly opposite of him (once you completed the quest).
It is speculated he was one of the men in the Fallen Hero of the Horde's group while venturing in the Blasted Lands and got killed.