Death is a major cosmic entity found in the Vertigo imprint of DC comics, though by the very nature of cosmic entities she is part of the larger DC cosmology alongside her siblings, known as the Endless - each of whom embody fundamental forces of creation far beyond even the sphere of the gods.
Death is the embodiment of both life and death, in contrast with many other anthropomorphized versions of Death, thus it is her who both ends life and begins it, all creatures will inevitably be visited by Death and it is stated that when the multiverse itself comes to an end it will be Death who will be left to destroy Destiny, then "lock up shop" and "put away the keys", effectively ending creation itself.
Like many depictions of Death she is neither fully malicious nor benevolent and is instead a neutral being, though unlike the highly manipulative Death of Marvel cosmology DC's version is often more open in her dealings with mortals and while dangerous due to her sheer power she is rarely as interested in opportunistic grabs for power.
Death of the Endless is not the only entity that lays claim as the embodiment of death in DC cosmology; others to claim the title include Nekron, the Black Flash and the Black Racer.. however it is worth noting each of these character embodies a *specific* aspect of death while Death of the Endless embodies all aspects of both death and life, making her much more powerful than her "competition" (though they may also simply be different forms she takes, as is common with cosmic entities).