Web fiction
Mary Sue
Fan fiction's pejorative for a character, usually a young woman, perceived as unrealistically free of weaknesses or flaws.
A Mary Sue is "a type of fictional character, usually a young woman, who is perceived as unrealistically free of weaknesses or character flaws," often read as wish fulfillment for the author. The name comes from the heroine of Paula Smith's 1973 parody "A Trekkie's Tale," published in the Star Trek fanzine Menagerie, which skewered the idealized teenage officers common in fan fiction of the time: adored by the canon cast, central to every crisis, often dying a hero's death. Male equivalents go by Marty Stu or Gary Stu.
The label is pejorative and notoriously elastic. Tisha Turk's verdict is often quoted: "ultimately the reader, not the author, defines a Mary Sue." Critics have noted the term gets applied to nearly any competent heroine, which silences writers. The usable craft takeaway is diagnosis rather than fear of capable characters: flaws that cost something and genuine growth, the material of character arcs, are what keep a protagonist from reading as an idealized self-insert.