Obtain the Mark of the Lightbringer and return it to Mehlar Dawnblade at the Bulwark in the Western Plaguelands.
I was once a pupil of Uther Lightbringer, founder of the Knights of the Silver Hand. I saw how he mishandled Prince Arthas's training. It led to the destruction of my homeland, Quel'Thalas, and I blame Uther and his incompetence for all of it! And now he has a tomb in his honor - how lovely.
My sources tell me that the scarlet fools are keeping one of his 'holy' relics atop their guard tower near the gates of Hearthglen.
Go to the Western Plaguelands and retrieve it for me.
When you've managed to retrieve his 'mark', we're going to change it a bit; make it better.
The first step is complete. Hand me the Mark of the Lightbringer and I will transform it into something more suitable.
Then my revenge will begin in earnest, <class>!
The Bulwark is actually located in Tirisfal Glades on the border with the Western Plaguelands.
The guard tower is located at (55,23) on the road leading to Hearthglen, at the bend prior to the gates. The Mark is in a chest (Holy Coffer) on the top level, guarded by 3 NPCs.