From WoWWiki

Nerubian viziers are creatures that can be encountered in the upcoming WotLK expansion.

The half-spider, half-humanoid viziers once served as advisors, sorcerers, and seers to the mighty nerubian spiderlords. But in the aftermath of the War of the Spider, the tables turned, and in the vacuum of their collapsed society, the cunning viziers rose to power. Utilizing their sorcery and high intelligence, the viziers have emerged as the rulers of the Nerubians' underground kingdom.

It is rumored that the viziers themselves may serve an unseen emperor, one who is destined to lead the ancient spider-people to a final victory over the Scourge. While many can only speculate as to the existence of this nerubian emperor, some continue to investigate the link believed to exist between the nerubians and the vicious insect race known as the Qiraji.

Speculation

This article or section includes speculation, observations or opinions possibly supported by lore or by Blizzard officials. It should not be taken as representing official lore!

Nerubian viziers may have same role as qiraji prophets, due their same look and "intelligent caster" profile. It is speculated the unseen emperor is an Old God or a new Nerubian who dwells in Azjol-Nerub.