Reapers are the servants of Death. They assist in maintaining the Natural Order and are completely neutral, aligned with neither Heaven, Hell, nor Purgatory. Reapers are required for death to occur, they wait till a person meets the end of his or her life (either through accident, or simply the natural end point of that person's life) and then touch the person causing them to die.
Reapers are completely neutral beings, not caring for deals, fate or even each other at times, all they care about is maintaining "Natural Order" of life and death. Although sometimes uncaring, Reapers generally sympathize with their victims, but refuse to make allowances, regardless of who or why.
Reapers are seen as a collector of souls, the messengers of the dead and most important of all the guides that came to all mortals. It was not the Reaper's place to judge souls, nor was it the entity's role to aid or hinder mortal affairs. Put simply the Reaper's task is to appear to the dying and guide them to their final destination where they would be judged accordingly by higher powers.
Although the Reapers normally comes to those already dying it has been noted that on rare occassions Reapers have the power to kill someone, though the entities rarely (if ever) do this out of malice. Due to the Reapers appearing in a vaguely human form there are many tales in which these beings can be tricked or bribed into freeing a person (which is where the phrase "cheating death" likely came from). For the most part, however, Reapers were seen as unable to be reasoned with and an inevitable part of being human.