Obrahiim, the Traveler

From WoWWiki

Originally just another skeleton, Obrahiim, the Traveler quickly proved himself as more than a mere grunt and rose through the ranks to become an advisor to Kel'thuzad himself. A brilliant architect, he played a pivotal role in the conception of Naxxramas and later in the creation of Acherus. Much of his inspiration was taken from nerubian architecture and the magics practiced by Orcish warlocks, but he always strove for more knowledge. He disappeared several years ago after leaving to study the ruins of Zin-Azshari.

Obrahiim is mentioned in the "Compendium of Fallen Heroes" found in Acherus and is considered a hero by the Scourge.