It was inevitable that this topic would come up, as it’s one of the most common topics when it comes to characters and plot out there. Yes, it’s time to look at Mary Sue and her Spear Counterpart, Gary Stu. So much has been said that I don’t feel it’s necessary to recount all the details as I normally would. I could go over all the common Mary Sue and Gary Stu markers, all the usual tell-tale signs you can find all over the internet. Even better, I could put together yet another Mary Sue litmus test so that you can wind up doubting your characters and writing. Instead, I’m going to go into the true problem with the ‘Mary’s and ‘Gary’s and how it extends past a simple list of characteristics.
I myself generally just read the lists and listened to the tests myself until, a few days ago, I would up reading some more in-depth analysis of the Mary/Gary character on a couple of sites that got me thinking more analytically about it. All of that led me to this important conclusion: A Mary Sue or Gary Stu isn’t one by their common characteristics (though those may contribute). The real determination of what is or is not a Mary Sue or Gary Stu revolved around their effect and place in the plot of the piece.
By dint of their very existence, a Mary Sue or Gary Stu warps the plot and turns all (or a majority) of the events in a plot line to be about themselves. The description of the character, no matter the unusual characteristics, ‘kewl’ powers, purple prose details, or exotic and tragic background, has little effect on this, other than to provide obvious markers. The most insidious and damaging Sues/Stus are the ones that have the serial numbers filed off, so to speak, leaving the reader in an even greater sense of dismay as the totally normal and average person becomes the pivot of an entire literary world’s plot lines.
Take, for example, a perennial writing critic punching bag, the Twilight series. I’ve actually read it, so … yeah … this isn’t coming from a misinformed viewpoint. The main character, Bella Swan, is a Mary Sue …. really she is! But not because of looks or talent or skills. In fact, she has plenty of informed flaws: clumsy, supposedly plain, that sort of thing. However, despite her ‘flaws’ and ‘normal’ stature, everything in the plot revolves around her. She attracts admirers by the handful (including normal boys before Edward sees her), all major action turns around her, entire conflicts are fought over her, and she becomes the pivotal piece later on. On top of that, she is revealed to have unique properties, becomes a better vampire than most every other vampire almost overnight once she’s turned, and has the unique child that becomes the plot point of the third book. No matter how normal or plain or clumsy or average she is depicted to be, in the end, Bella becomes the center of that literary universe and nothing of import happens unless it involves her or targets her.
Now, you could argue that is the case in most pieces that center on one main character. To a degree, you may be right: Obviously much of a book may pivot around a single main character. However, a non-Sue/Stu lead will not have EVERY thing in the plot be all about her/him. Other characters retain agency and make decisions and events can alter the plot that have nothing to do with the main character. It is keeping that sense of universal free will and character agency that truly differentiates a piece with a strong lead character versus a piece with a Sue/Stu lead character.
A final good indicator of Sue/Stuness that lies outside of character traits is a study of the character’s arc. Does the character in question follow an identifiable characterization arc during the piece? Do they change, grow, or regress in reaction to the events of the plot and their choices in it? If there is a real character arc and the character changes over the course of it, the character is likely a fine one. It is the Sues and Stus that are most often immutable. After all, why should they change when they are, or are thought of by their authors, as in the right, or perfect, or infallible, whatever superlative you wish to use?
So, to me at least, what makes a character into a Mary Sue/Gary Stu is, in the end, their toxicity to the plot and the piece over all. Understanding this can let you create a unique character, perhaps one very exotic for the setting of your piece, but still dodge the Mary Sue pitfalls and make that character a special and intriguing one. Remember, you don’t have to be totally mundane to avoid Sue/Studom!