The Silence

The Silence  was a mysterious species that forced the Doctor's TARDIS to explode on the date of June 26th 2010, and thus created cracks in time that would erase various things throughout the universe, and eventually the universe itself.

Biology
The Silence were depicted as tall humanoids with bulbous heads and grey, mouthless, skeletal-like fleshy faces. Their hands possessed large, elongated fingers. They spoke in low, guttural voices and tended to make growling or clicking noises. (DW: The Impossible Astronaut)

Powers and abilities
If anyone saw one of them properly, they would instantly forget as soon as they looked away. In addition, they seemed to be able to move from place to place very quickly. The Silence could also use an energy discharge from their hands to kill and obliterate someone, leaving only ashes behind. It appears that they have to draw this energy from an outside force though, as when performing this act the energy from the lights flew into it. When absorbing the energy and discharging it, a sort of mouth or hole appears where a mouth should be. (DW: The Impossible Astronaut)

History
The Silence first took control of the TARDIS in 102 A.D. They forced it to land outside of Amy Pond's house on June 26th 2010, and it began to explode shortly afterward, trapping River Song inside of it within a time loop until the Doctor saved her. 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/The Big Bang). 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 Earth. (DW: The Vampires of Venice)

The Silence were apparently present on Earth for hundreds of years, going unnoticed by the human race. One of them spied on the Doctor, Amy, Rory, and River in Utah, 2011. Another one visited the White House in 1969 and killed Joy in front of Amy Pond. (DW: The Impossible Astronaut)

The Silence may have created the TARDIS from The Lodger as River and Rory find a base full of the Silence and the same or similar room with the console seen in that episode.

Behind the scenes

 * Marnix Van Den Broeke portrayed the Silence in The Impossible Astronaut and Day of the Moon
 * Monsters created by Steven Moffat are usually designed to make something mundane and everyday into something terrifying (stone statues, gas masks, shadows). In one sense, The Silence stray from this pattern because they are distinctly alien-looking, with large, bulbous heads and elongated fingers. In other ways, The Silence stay with the pattern of turning the mundane into the terrifying in that they wear human-style suits and ties, and are said to be responsible for that "something in the corner of your eye, a creaking in your house, or voices through a wall" (DW: Day of the Moon) which are everyday occurrences that humans experience.