The Earthen Ring quartermaster is a vendor found in one of the first zones you can visit in World of Warcraft: Cataclysm. As the name suggests, they're tied to the Earthen Ring faction and sell a variety of goodies to those who have earned sufficient reputation levels to unlock them.
Daily quests play a big role in Cataclysm's endgame, and allow you to raise your reputation level with the faction residing in each area. Earthen Ring is found in Vashj'ir, for example, so you'll need to make your way to that underwater zone if you want to complete the quests and track down its vendor.
If you don't have the seahorse mount, it's worthwhile grabbing it while you're there, as it will make traversing the region and reaching the location of the Earthen Ring quartermaster that much easier.
The Earthen Ring quartermaster, Provisioner Arok, is found at Silver Tide Hollow in the Shimmering Expanse. I've marked the location on the screenshot above, but the Vashj'ir map can be difficult to read. If you have trouble locating the opening to the cave, approach the area from the east and look for the large yellow tubular flowers near the entrance.
Once inside, you can climb out onto dry land, where you'll find the Earthen Ring quartermaster standing near the fire. He sells some gear items that you can use while leveling, though more importantly, he has a few pieces of epic quality equipment for max-level players. You'll need to reach the Exalted reputation level with the Earthen Ring faction to buy these, however.
Completing the quests in Vashj'ir will generally reward reputation but finishing the entire zone's storyline will unlock the daily quests for the Earthen Ring faction once you hit level 85. This will then let you earn daily reputation with each hand-in. You can also pick up the Earthen Ring Tabbard from the quartermaster once you reach the Friendly reputation level, which you can wear to earn reputation for killing bosses in Cataclysm dungeons.
