In His House He Waits Dreaming (10 player)

For those who think that the posters above are high, the whole idea of the forgotten ones (first seen on Warcraft 3: The Frozen Throne), Old Gods (such as C'thun from AQ) and even Murlocs are nothing but a tribute to Howard Phillips Lovecraft, Creator of Cthulhu mythos (C'thun is a reference to him).
In The Dunwich Horror Lovecraft talks about someone something named Yog-Sothoth (Yog-Saron being its tribute):

Yog-Sothoth knows the gate. Yog-Sothoth is the gate. Yog-Sothoth is the key and guardian of the gate. Past, present, future, all are one in Yog-Sothoth. He knows where the Old Ones broke through of old, and where They shall break through again. He knows where They have trod earth's fields, and where They still tread them, and why no one can behold Them as They tread.

Now on to the achievement:

Cthulhu is depicted as having a worldwide cult centered in Arabia, with followers in regions as far-flung as Greenland and Louisiana. There are leaders of the cult "in the mountains of China" who are said to be immortal. Cthulhu is described by some of these cultists as the "great priest" of "the Great Old Ones who lived ages before there were any men, and who came to the young world out of the sky."

The cult is noted for chanting its horrid phrase or ritual: "Ph'nglui mglw'nafh C'thulhu R'lyeh wgah'nagl fhtagn,"

which translates as

"In his house at R'lyeh dead C'thulhu waits dreaming."

In his house at R'lyeh dead C'thulhu he waits dreaming.

-Amorim

Ph'nglui mglw'nafh C'thulhu Yog-Sothoth Yogg-Saron R'lyeh Ulduar wgah'nagl fhtagn

That is not dead which can eternal lie. And with strange aeons even death may die.