As was pointed out yesterday, quite a few old faces are returning in Wrath of the Lich King. The Scarlet Crusade, The Venture Company, Arugal, etc. Most of them make sense in the context of the events in Northrend, but on the other hand, a couple of them might be inspired by pure fan service. That's totally okay, don't get me wrong. I loves me some fan service. If simple worgen love is what brought back Arugal, I most certainly will not complain.
Let's pretend for a moment that we could bring back any lore character for Wrath of the Lich King. Blizzard just walks up to you and says, "Hey, who do you want to see in Wrath?" They can be dead or alive, a major character or a minor NPC, whatever you want. If you could do that, who would it be?
My choice would be Justinius the Harbinger. Bring him to Northrend to kick in the Wrath Gate guarding Icecrown with his tauren friend Melgromm Highmountain. If you don't know who Justinius is, he's the super-awesome Draenei Paladin fighting the Burning Legion at the Stairs of Destiny, just beyond the Dark Portal. He looks quite awesome in his Judgement Armor, plus he's an all around cool guy. Just go watch him in action for a few minutes. He doesn't take crap from any demon.