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.