Golgarok is a non-elite hostile level 83 HUGE elemental rare spawn with approximately 134k health who spawns in the Quaking Fields in the most south western part of Deepholm. The location he can be found at is shown in green on the map below. He is easy to spot compared to the other giants in the area because he has a pinkish coloring.
Golgarok drops Golgarok's Tenderized Treads, which are bind on equip item level 333 cloth boots. On my server they sell for approximately 400 gold. He also drops around 20 gold, and I imagine for leveling characters killing him yields a hefty amount of experience.
Be careful when you take him out! There are a lot of giant elites patrolling in the area. If your level 85 it shouldn't be a problem, but at lower levels it easily could be. As you can see in the video below i accidentally backed into one...oops.
Other than being careful for the elites in the area and other non-elite mobs, Golgarok himself isn't too difficult. Interrupt his earthquake if you see him channeling that. Loot. Profit.