The sources we have that tell the stories of the gods and heroes come from many different authors from different parts of the Mediterranean world and from different points in time, spanning several centuries. Cultures and beliefs change over the course of a few decades, let alone centuries, so their stories adapt too. But with these myths, even within the confines of ancient Greek culture, each author had some artistic freedom to reinvent the story and make it more applicable or interesting to his audience. In this way, myths function similarly to comic book heroes, like Batman. Every author who tackles the story of Batman’s origin has to bring something new to it or it gets boring. There are some important elements that have to stay the same (like Bruce Wayne’s parents are killed when he is young as they leave the opera), but other elements can change (like the 1989 Tim Burton film, which makes Jack Nicholson’s Joker the man who killed Bruce’s parents). In the same way, the different authors who wrote versions of the Greek myths took liberties with various aspects of the myths, even though (for the most part) the main outlines of the stories remained the same. Thus, even though the Greek myths were in a very real sense sacred stories, in this respect they were more like modern literature, films, or the stories of comic book heroes than the Judeo-Christian Bible.
Mythology Unbound: An Online Textbook for Classical Mythology by Jessica Mellenthin and Susan O. Shapiro is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.