Griegen is a level 75 rare elite spawn with approximately 16k health. He can be found on the western side of Zul'Drak in several different locations which are indicated in orange below. Griegen is one of four rare spawns in Zul'Drak. The other three are Zul'Drak Sentinel, Gondria and Terror Spinner.
This npc is part of the Northern Exposure and Frostbitten achievements. He drops Ethereal Terror Handwraps which are level 74 bind on equip leather gloves with a random enchant. Like other Northrend rares, he also drops Abandoned Adventurer's Satchel, which generally contains about 20 gold, a full stack of frostweave cloth, and often times a few crystallized elements.
Although Griegen is elite, he should be a cakewalk to kill for anyone that happens to be questing in the area. He also awards a fairly high amount of xp for characters around his level.