Superhero comics are a unique genre in that most of its characters exist in a relatively ongoing-yet-static state, but are defined by hundreds of different writers and artists. So although most characters have some kind of foundation of who/what they are supposed to be on paper, that base is subject to the interpretation or reinterpretation of whichever creator is using the character in any given story.
If a character is around long enough, or achieves enough popularity/exposure, he or she will have stories that define them in the eyes of fans and other creators. Tales that will cement who they are and what they're about, or perhaps reinforce who they are and what they're about if the character had strayed too far or had been deconstructed in some capacity.
Or sometimes they're just really good stories that fans and creators embrace and, from then on, will point to and say: "There! THAT is what this character is all about!"
And sometimes there will come a story that redefines a character and changes the way they are seen. A deconstruction, a reconstruction, or maybe the creator just saw something in the character no one else ever had.
Sometimes it might be unintentional and even detrimental to the character.
Arguably, one of the best examples of a defining story that permanently shaped (or re-shaped, depending on your point of view) a character would be Frank Miller's The Dark Knight Returns. The impact of that title on Batman is still felt to this day. See also Year One.
Another less radical example might be Grant Morrison and Frank Quitely's All-Star Superman—a tale many fans I've seen point to as a perfect encapsulation of everything Superman is, should be, and represents.
And Wonder Woman?
She's certainly had strong, defining stories over the years. If asked, most fans will point to the runs of George Pérez, Greg Rucka, and Gail Simone or specific stories like The Hiketeia.
But there's one book that has influenced how she is regarded in the eyes of fans and creators since its release that usually isn't included when people discuss defining Wonder Woman stories. Largely because it isn't really a "Wonder Woman" story to begin with.
That would be Mark Waid and Alex Ross's Kingdom Come.
Usually, when this story is discussed, it's more in regard to Superman and maybe Batman. Superman especially is very much the heart of the story.
But Kingdom Come is a seminal and defining work for Wonder Woman, even if it wasn't intended to be. It marks a significant turning point for her—both in her portrayal, and her place in DC as a whole—and for better or worse, has defined her in many people's eyes. Whether they realize it or not, it has colored the way Wonder Woman is presented, and its impact on her remains to this very day.
