The Silence
From Tardis Wiki, the free Doctor Who reference
"The Silence" is a title based upon conjecture.
Check the behind the scenes section, the revision history and discussion page for additional comments on this article's title.
The Voice describes an unknown, but powerful entity that forced the Doctor's TARDIS to explode, and thus created the cracks that would erase the Universe. (DW: The Pandorica Opens/The Big Bang)
Although the entity behind the voice was never visible or named, it was heard to be speaking before the TARDIS exploded, saying: "Silence will fall." (DW: The Pandorica Opens)
It is rumored to be Omega
