Mary Sue is a negative term used in fanfiction and literary criticism to describe an original character that is often overly idealized or assumed to be a projection of the author. When used by a male author, the character is referred to as a Gary Stu or Marty Stu.
The name “Mary Sue” is taken from a character that appeared in Paula Smith’s parody Star Trek fanfiction titled “A Trekkie’s Tale.” Originally published in the December 1973 issue of the fanzine The Menagerie, the 200 word piece intended to critique the abundance of Star Trek fanfiction Smith saw in which adolescent girls become the youngest member of the Starfleet crew whom every canon character fell in love with. It was paired with a drawing of wide-eyed young girl with braces to illustrate what the character would have looked like.
“Gee, golly, gosh, gloriosky,” thought Mary Sue as she stepped on the bridge of the Enterprise. “Here I am, the youngest lieutenant in the fleet – only fifteen and a half years old.” Captain Kirk came up to her.
“Oh, Lieutenant, I love you madly. Will you come to bed with me?”
“Captain! I am not that kind of girl!”
“You’re right, and I respect you for it. Here, take over the ship for a minute while I go get some coffee for us.”
Mr. Spock came onto the bridge. “What are you doing in the command seat, Lieutenant?”
“The Captain told me to.”
“Flawlessly logical. I admire your mind.”
Following its publication, Smith went on to speak at some of the earliest fandom conventions, cementing the definition of a Mary Sue to be a wish-fulfillment outlet for the author which can sometime seem out of place in the established universe and ultimately warps the canon characters’ personalities, causing them to act out of character.
In March 1999, author Pat Pflieger presented a paper titled “Too Good To Be True: 150 Years of Mary Sue” at the American Culture Association conference. Pflieger traces the history of these characters prior to the term’s 1973 coinage, marking that these types of charactesr have appeared in literature since as early as the nineteenth century, using examples of stories published in the children’s magazine Robert Merry’s Museum throughout the 1800s. Both characters from these stories as well as ones from 20th century fanfiction shared traits including idealized beauty, tragic pasts, charming personalities and a desire to fix things the author deems “broken,” whether that be feelings or canon stories that did not live up to expectations. The paper lists 30 different characters written between 1849 and 1999 that could fit into the Mary Sue archetype.
In 2002, the LiveJournal community The Mary Sue Report was founded to highlight fanfics that featured Mary Sues, linking to the original story and highlighting the characteristics that fit the archetype. The following year, The Canon Sue Report was created to feature characters outside of fanfiction that could be considered Mary Sues, including Rose Tyler from Doctor Who, Maito Gai from Naruto and Lana Lang from Smallville.
Writing guides on avoiding creating Mary Sue characters can be found on Yahoo!, Salon and Fiction Press. Additionally, a Mary Sue Litmus Test exists for a writer to answer questions about their fictional characters to determine whether or not they would fall into this archetype. Discussion on Mary Sues can be found on Tumblr, TV Tropes and the Fanlore wiki.
As early as 1994, the term Mary Sue was seen as a blanket term for any heroine featured in a Star Trek fanfiction, with author Camille Bacon-Smith noting that it reached a point where writers were restricted for fear of creating a character that would be considered a Mary Sue. Research completed by J.M. Frey in 2009 found that these characters, though often hated by community members, can be stepping stones for writers trying to find their place in the fandom. Frey determined that self-based characters can be used as a tool for writers to understand ones self. The following year, Geek Feminismcompiled several blogs found on their link sharing group of writers automatically condemning original female characters to be vapid, noting that readers too readily dismiss a female-written piece with original characters on similar grounds.
The notion that Mary Sues are only disliked for being female was also discussed on book review blog The Zoe-Trope in May 2011, in which the author defines key traits about the Mary Sue archetype:
1) A character who is based, at least partly, on the author
2) A character whom has no significant flaws (except possibly ones the other characters find cute)
3) A character to whom everyone within the story reacts as if they were beautiful and wonderful except characters who are clearly evil and/or motivated by jealousy
4) A character with whom, during the course of the story, every available character of the opposite (and occasionally the same) sex will fall in love given any contact whatsoever
5) A character who undergoes no significant growth, change or development throughout the story
After the success of the Twilight series in 2008, many readers argued on personal blogs that Bella Swan was a Mary Sue character. The discussion was continued on Cracked, Yahoo! Answers, and peer-reviewed contemporary culture journal Reconstruction, though no conclusion was made.
 The Zoe-Trope – You Can Stuff Your Mary-Sue Where The Sun Don’t Shine
 Yahoo! Answers – Do you think Bella Swan from Twilight is a Mary-Sue?