I've toyed with the idea quite a bit. Death would spend quite a bit of time in the Negative Energy Plane, of course. I was thinking of having Death manifest as a largely shapeless form - if people were at the scene of a great slaughter, they might feel a dark, chilling breeze as if some terrifying entity had just traveled through them.
Death wouldn't necessarily be evil in my depiction, but more of a force of nature, which is why he inhabits an energy plane instead of one of the lower planes. Naturally, I've also considered more direct manifestations of Death - a dark form with a cloak, perhaps with hands of pure bone protruding from the sleeves so he can hold his vorpal scythe that seems to suck in and destroy light with its deeply negative energy (so even if you don't get vorpalled, Death usually hits, so you have a rather high chance of getting level-drained). Death, being a force of nature, wouldn't die very easily, and if worse came to worse, he's in charge of who dies, so I figured he could just not let himself die. You'd have to somehow take charge of his portfolio, at least in part, to kill death.
I haven't given much thought as to how that would happen, because I wouldn't consider it unless I had a party full of deities who were interested in the idea. Something that I have considered, but never done, that additionally wouldn't necessarily require deity status, would be to somehow pilfer Death's scythe, which would have the interesting effects of giving the party an item of unimaginable power and making a rather lethal enemy.
What I would need to consider more is whether or not the scythe is the source of Death's portfolio. If so, stealing the scythe would have the interesting consequence of preventing anyone from dying (unless the PC's figured out how to wield Death's powers, which if that would be possible, would probably require an ungodly amount of knowledge in arcana, religion, and the planes - probably enough that if the party hadn't specialized so that if they didn't have it maxed out by the time this adventure was possible, they wouldn't figure it out).
An alternative that occurs to me now is if the party talked to a noble cleric, an exemplar of shining goodness, who explained at length the unfairness of death and dying, and convinced the party to collect the scythe of Death, explaining how such a feat could be done. The party would get the scythe and give it to this fair and noble cleric, who would then reveal his true colors and escape (perhaps in the manner of the 2E scythes the tanar'ri used to cut open rifts to other planes), and so, to end the truly epic slaughter that the actually-evil cleric is unleashing, the party would have to make an interesting alliance with Death. That would put the feared end of life in an entirely new light, and everyone would know that there's a truly fearsome BBEG at the end of the yellow brick road.
I didn't get into fantasy and sci-fi movies/books and such until midway through the 90s....
