Seen this wizard (or these wizards) around lately? It's Archmage Vargoth. Actually, it's an image of Archmage Vargoth-- the guy himself is locked, by Kael'thas, inside the Violet Tower up in Netherstorm. The image is summoned with a staff obtained from a long quest chain that starts in Area 52. At around the third quest in the chain, you can obtain Vargoth's staff, which lets you summon an image of him which actually works as a questgiver for the rest of the chain (the eventual end of the chain is to get him out of the tower, though some players say it's not working correctly).
In fact, as long as you have the staff, you can summon him again. And again. And, yes, again. And you can do it anywhere. This guy had a little Vargoth party in Karazhan, and Vargoth has been popping up all over Azeroth-- in the captial cities, and even in battlegrounds. The only drawback is that the staff has a 2 minute cooldown on it, and so does the image-- you can't summon more than one at a time with just one staff. But if you have more than one player with the staff, Vargoth clones can appear, which means with a little coordination, he can become a very familiar face around Azeroth.
Until it gets "fixed," that is-- chances are that Blizzard will attach a location to the staff, only letting you summon him close to the tower where he's trapped. But until then, I can't wait to see this little purple wizard in as many unexpected places as possible.