Tsul'Kalu is a level 28 non-aggressive rare gorilla that can be found to the west of the Venture Company Base Camp just across the river in Northern Stranglethorn Vale. (I have indicated where he can be found in red on the map below.) He is one of the three troll gods: Pogeyan <The Fire Spirit>, Mahamba <The Water Spirit>, and Tsul'kalu <The Earth Spirit>. He shares the same model and coloration as Unk'loc a level 53 rare spawn in Un'Goro Crater, but unlike him he is tamable at only level 28.
Tsul'Kalu can be found with NPCScan. You will need to add it, his NPCScan ID is 51661.
You can also use this macro to help find and tame this guy:
/cast Tame Beast
He always spawns in the same location and never patrols far. Hes also very easy to spot as he is a HUGE gorilla with an earth shield around him.
Tsul'Kalu's spawn timer seems to be anywhere from 3 hours to 6 hours since he was last tamed or killed. He does not share a spawn timer with the other two troll spirits, all three of them can be up at the same time.