The Silence


 * You may be looking for the unnamed species currently called The Silence.

 was a religious order. Their core belief was that "silence will fall when the Question [was] asked" — "the question" being the the oldest question, the very first question of the universe.

Beyond this core belief was the significant goal of killing the Doctor, whom the Silence felt interfered with their central tenets. (DW: Let's Kill Hitler)

The order and the Doctor
The Silence made many attempts upon the Doctor's life. It was they that forced the Doctor's TARDIS to explode on 26th June 2010, creating cracks in time that would erase things throughout the universe, and eventually the universe itself. It is not known if the destruction of the universe was actually part of the Silence's plan. Although the entity that caused the Doctor's TARDIS to explode was never visible or named, a voice was heard speaking before the TARDIS began exploding, saying: "Silence will fall!" (DW: The Pandorica Opens / The Big Bang)

The Silence also indirectly played a hand in the destruction of the Saturnynians' homeworld. In 1580 Venice, Rosanna Calvierri said that through some of the cracks, the Saturnynians saw only silence and the end of all things. This caused them to flee their homeworld to 1580 Earth through a different crack that acted like a wormhole. (DW: The Vampires of Venice)

The Silence were also behind the Battle of Demons Run, as well as the kidnapping and brainwashing of a young River Song. She then made several attempts on the Eleventh Doctor's life. Ultimately, she successfully introduced a poison into his system which would most certainly have killed him, had she not broken free of her conditioning and offered him the sum of her regenerative energy. (DW: Let's Kill Hitler)