High Thane Jorfus is a level 80 rare Ymirjar with approximately 18.9k health. He can be found patrolling in three different areas in Icecrown. These locations are the Court of Bones, Sindragosa's Fall and the Fleshworks. (These patrol areas are indicated in blue on the map below.) He is one of three rare spawns in this zone. The others are Hildana Deathstealer and Putridus the Ancient.
High Thane Jorfus is part of the Northern Exposure and Frostbitten achievements. He drops Corroded Faceguard which is a level 76 bind on equip plate helm 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. He's also worth a hefty amount of experience for people leveling in the area.
He is very easy to notice when he's up because he is HUGE; not anywhere near as big as Putridus, but still quite large compared to everything else in the area.
He is also a fairly easy kill for those who come across him while leveling.