Archmage Lan'dalock in Dalaran wants you to return with the Axe of the Plunderer. This quest may only be completed on Heroic difficulty.
I need you to assemble a group and lead them into Utgarde Keep. Therein, you are to find and slay Ingvar the Plunderer before he can lead his vrykul forces to sack the nearby Alliance and Horde towns.
I require his axe as proof that he has been dealt with. It's not that I don't trust you. It's simply prudent to be certain that the deed has been done.