Reapers are enemies Diablo III. They are undead soldiers, created by Malthael's death power once embraces Aspect of Death.
They are secondary antagonists in Reaper of Souls.
The Reapers were a macabre combination of ghastly spirits and baleful constructs. The force was primarily led by angels, with undead and other thralls serving under them. Information on the Reapers is scarce as most who encountered them perished. The Horadrim Lorath Nahr was an exception, and he took notes of the Reapers he encountered where no one else could.
Some reapers are formerly living things in Sanctuary, notably Westmarch Hounds(canines), Exorcists (master of demon depossession whom reanimated), and Revenant Soldiers. How these Sanctuary Reapers created revealed when Nephalem heroes and his friends discovers piles of fallen warriors revived by angelc reapers somewhere in Westmarch during their siege.
Reapers of angelic origin are quite different from their relatives of the High Heavens. Many Reapers show pale, tangible skin, and some (like Anarchs) even have faces, although those appear like eyeless masks with disfigured facial features and a menacing grin. Others, like Death Maidens, are translucent and composed of ethereal streams. Tangible Reapers also have dark red blood (as opposed to the glowing blood that angels usually possess). Many of the angels in Reaper ranks are very similar to regular angels, but some (like Ghastly Seraphs) are changed beyond reason. The majority of angelic Reapers either lose their wings, or display the skeletal and gray remnants of them.