A Mary Sue character is an overly perfect character and/or a character that is clearly a glorified projection of the author herself. The are male versions of Mary Sue. They are known as Gary Stu or Marty Stu. A Mary Sue character is usually an undesirable character. Even your heroes need flaws. An impossibly perfect character makes your story less plausible and less believable.
The origin of the Mary Sue term can be found in fan fiction. Know Your Meme traces that origins to a parody of Star Trek fan fiction called "A Trekkie's Tale." This short tale by Paula Smith described a young female character (Mary Sue) that was a critique of a character she frequently observed in Star Trek fan fiction from 1970s zines. The character created by Smith has evolved into Mary Sue coming to mean any character that is too perfect, too beautiful and wise beyond her years. TV Tropes expands on the Mary Sue concept with other types of Mary Sues, such as the Anti-Sue. They also note that what classifies a Mary Sue character has become more and more difficult to nail down due to its increasing use.
The Wikipedia entry for Mary Sue notes that there has been same criticism or backlash at the concept. One major criticism is that beginning writers might be hesitant to write out of fear of creating a Mary Sue. Fear of criticism is never a good reason to not write. You have to practice to get better. Some writers practice by putting themselves - or a perfect hero - into situations. There is always time for editing if you have written a story that is centered around a character that is too perfect. Young authors also shouldn't worry too much as the term Mary Sue is now also used as a trolling attack and trolls should be ignored.
Mary Sue Tests and AdviceIt should be fairly obvious to you that you have an overly perfect character. There are tests that can help you make sure your character is not a Mary Sue. The ultimate decision about your characters is always yours. If your character ticks the boxes of all the adjectives below they are certainly crossing into Mary Sue territory. If you have created a Mary Sue then at least put her up against an equally perfect villain to make your story interesting.
Here is a list of some of tests and articles offering tips for avoiding creating Mary Sues.
- The Universal Mary Sue Litmus Test - This is very detailed questionnaire that will give you a score and tell you the chance your character is a Mary Sue. If you score very low you might even have an Anti-Sue.
- Is Your Protagnist A Mary Sue? - 40 questions that can help you determine whether you have created a Mary Sue or not
- Mary Sue Test - this type provides 42 questions to analyze whether or not you have created a Mary Sue.
- Is Your Character a Mary Sue? - This is article helps you identify signs that you character might by a Mary Sue and offers advice for making your characters more realistic.
- OC Mary-Sue Test 2.1 - a Mary Sue test for original characters