Discworld/Mort/Analysis

Mort was created by Pratchett to flesh out Death as a character
Much like "Guards, Guards" served to make Lord Vetenari a more complex character than his one dimensional references in eariler books indicated, this book was written to give the character Death added character.

However, instead of doing so entirely through Death's eyes, he used an Audience Surrogate in Mort, who is very much alive but has a name that means "death", so as to not have to blatantly retcon everything done through Death's POV up to that point, and also so he could give Death Character Development in a natural way by having Mort serve as a Foil, and the changes done by using this method led to Death being seen as more three dimensional since due to character interactivity in this book being used as a narrative springboard.