Archmage Khadgar

When first picking up the quest in someplace other than the Blasted Lands, e.g. the Shrine of Seven Stars, the quest dialogue is as follows:

<The archmage focuses intently on the portal.>

Look. Their numbers are abating, however briefly. This may be our chance.

Are you prepared to face whatever's on the other side of that portal?

FOR AZEROTH!

When you click on it, a dialogue box opens up:

You are about to embark on a dangerous mission, and you may not be able to return immediately. Are you sure?

Hit "accept" and you'll be teleported directly to Draenor. Keep your arms and legs inside at all times and don't trip!

When you meet him again at The Dark Portal he has turned into Archmage Khadgar

As of 6.2, Archmage Khadgar is only at the Blasted Lands location. That is what Blizzard originally intended.

When 6.0.3 first hit, there was a huge circus in the Blasted Lands because the servers were overloaded by too many people trying to click on Archmage Khadgar at the same time for Warlords of Draenor: The Dark Portal (the initial WoD breadcrumb quest). As a result of the bottleneck, Blizzard brought more servers online and created additional copies of Khadgar in Org, Stormwind and Pandaria. The additional copies were removed in 6.2, but Wowhead is still showing them.