Reapers are the main antagonists in the Doctor Who episode Father's Day. They were being linked to Time itself. They searched for temporal paradoxes. If the balance of time was disrupted, they would be drawn out in force to remove the offending element.
Reapers have a slightly resemblance to dragons with blackish scales and red eyes. They also have a scythe shaped tail and a mouth on their stomachs.
Time Lords had ways to keep Reapers at bay but after their disappearance in The Last Great Time War, there was nothing that could stop the Reapers from going through wounds in time.
One time The Ninth Doctor and his companion Rose Tyler travelled back in time to November 1987 where Rose saved her father Pete from being ran over much to the Doctor's dismay. Because of this, the Reapers appeared and devoured people including the Doctor but they were stopped when Pete decided to sacrifise himself to restore the balance of time and brought the Doctor and the Reapers other victims back to life.
Powers and Abilities
Whenever there a wounds in time, The Reapers will be able to break through wounds in time. The Reapers can fly using their powerful wings, They can use their mouth on their stomachs to consume people and they have sharp claws for ripping their prey apart.