Perobas the Bloodthirster is a level 71 rare worgen (the cool-looking model, not the ones you can play) with approximately 14k health. He can be found in northeastern Howling Fjord in a few different locations which are indicated in green below. He is one of three rares located in this zone. The other two are Vigdis the War Maiden and King Pin.
Perobas is part of the Northern Exposure and Frostbitten achievements. He drops Worgen-Scored Shackles which is a level 70 bind on equip mail wrist piece 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.
Perobas 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.