You’re approaching the outer edge of the spectrum when one of your characters is the personification of an event, but sometimes it works.
Death has had a busy literary career: being one of the first on the scene in religious tales, founding member of the Four Horsemen, topic of a Blue Oyster Cult song, ad nauseum. Dying and what does (or doesn’t) come afterwards is one of the most fundamental questions of the human experience. Yet in spite of his importance, some of his appearances just stink.
The danger is that if you make someone as iconic as Death as a secondary character, it can look like a cheat. He just can’t gallop in as your hero gasps his last and decree “It is not yet his time!” and set everything to rights. On the other hand, if he’s a main character what can he really struggle with that doesn’t seem trite or boring? It’s highly unlikely the reader will really be concerned about Death’s well being in regards to the ticking bomb under his chair.
The Seventh Seal
In this brilliant and haunting movie, Death is challenged to a game of chess by a Knight returning from the Crusades. Death is a man with a white face and a black robe, not an animated skeleton. He is clearly different from the other characters, but not graphically so. He is quiet and calm. Relentless in his approach, but not horrifying.
While playing chess, Death serves as a foil for the Knight’s musings about the world and his fate. Death isn’t intended to provide answers, but to instead allow the audience to better understand the Knight and the Knight’s quest for life’s meaning. It is Death’s subtle portrayal that makes him so effective.
In scenes where the Knight and Death make their moves, it is almost of two equals sitting across the chessboard from one another. This makes the Knight’s questions honest and sincere, and not the pleadings of someone cowering before an oppressor.
Discworld
It might seem that Terry Pratchett’s representation of Death in his Discworld series is on the other end of the spectrum from the Seventh Seal, but not at all. Discworld is a heavily satirical series of books, and Death is portrayed as a fully cloaked skeleton with all the classic accompaniments, including a scythe, hourglass, and pale horse (named Binky). Yet in spite of the light hearted tone, Death is a deadly serious character. He performs his task methodically, while struggling to understand the humans whose spirits he collects.
Death claims that his skeletal form is not his own, but is what people gave him by anthropomorphizing him. His home is all blacks and grays because he can’t quite get the hang of color. He keeps a manservant around for company, and once adopted a human daughter. Yet while being so riddled with quirks, all of these attributes make Death a foil for the discussions and events going on around him. In “Hogfather”, Death helps people understand the importance of belief, while in “Soul Music” he explores passion and obsession (and of course, Rock and Roll).
Yet even after making Death this human, Pratchett still created an adversary that Death struggled against - the cosmic Auditors. As great of a foil as Death became, there was still a need for that essential conflict that keeps a story turning, and not much challenges Death.
If you take your characters to this cosmic extreme, make them big but don’t worry about giving them much depth. Focus on using them to showcase the challenges and issues facing your other characters, and you can prevent someone like Death from killing your story entirely.