The concept of death as a sentient entity has existed in many societies since the beginning of history. In English, Death is often given the name Grim Reaper and, from the 15th century onwards, came to be shown as a skeletal figure carrying a large scythe and clothed in a black cloak with a hood. It is also given the name of the Angel of Death or Devil of Death or the angel of dark and light (Malach HaMavet) stemming from the Bible. The Bible itself does not refer to "The Angel of Death;" there is, however, a reference to "Abaddon" (The Destroyer), an Angel whose true identity is a mystery, as is the identity of "The Angel of the Abyss".
Originally a resident of Hell, Grim Reaper is an 'Undead, talking, magical skeleton.
He was worshiped by demons, skellatons, harpies, ghosts, and Goblins.
Grim's appearence stays true to the iconic image of the Grim Reaper; Grim is depicted an adult-sized 'undead, talking magical skeleton'. Grim is most often seen wearing a long black robe with a hood; the robes make him look thinner than he actually is.
Grim is also seen with his scythe, an object of power in the series and the source of most of Grim's powers.
The concept of Death as a personified being is timeless, being as old as time itself but the grim figure of a hooded skeleton carrying a scythe was not very evident until the medieval period - during a time where morality was seen as pivotal to society and fear of the unknown was high it was perhaps unsurprising that life's greatest mystery (death) would come to be vied in the medieval mind as frightening and ever-present: the ghostly phantom of Death became known in time as the Grim Reaper and although a neutral force was as feared in the past as it is today.
The Grim Reaper was seen as a collector of souls, the messenger of the dead and most important of all the guide that came to all mortals - it was not the Grim Reaper's place to judge souls, nor was it the entity's role to aid or hinder mortal affairs: put simply the Grim Reaper's task was to appear to the dying and guide them to their final destination where they would be judged accordingly by higher powers.
Although the Grim Reaper normally comes to those already dying it has been noted that on rare occassions the Grim Reaper has the power to kill someone, though the entity rarely (if ever) does this out of malice - due to the Grim Reaper appearing in a vaguely human form there are many tales in which the entity can be tricked or bribed into freeing a person (which is where the phrase "cheating death" likely came from).
For the most part however the Grim Reaper was seen as unable to be reasoned with and an inevitable part of being human - in biblical terms the Grim Reaper is considered one of the four Horsemen of the Apocalypse and although an essential part of current existence shall ultimately be cast into the fiery lake alongside the minions of Satan, granting humanity true immortality as a result.