Mary Sue

I'll just give a short summary of my understanding of who it is, but there are hundreds of sites dedicated to her; and though their collective opinion is somewhat different to mine, what they have to say is still valid.

Some say she is just one character, but I say she's more then that; she's a whole story. Mary Sue is an instant gratification instrument. People write it because they think it will be the greatest thing in history and everyone will love their character. The story normally revolves around the character instead of the plot.

Though Mary Sue is generally a female character it can be either. It's harder to spot Jack Stone (what I've named him but he also goes by Marty Stu and tones of other names) because he's a) less annoying and b) there's a distinct gender gap in the writers on Fan Fiction and (to a lesser extent) Fiction Press. In paradox more male authors are published and paid more.

Mary Sues are usually more whiney though not always and tend to be substantially younger (fifteen to twenty-one to unspecified but still gorgeous) then those around her; the youngest in her field and amazing all the father figures. If set in different eras she will have modern views on gender roles and be the inventor of numerus inventions. They tend to be insecure with the writer using other characters to praise the main character.

Jack Stones are older (mid-twenties to mid-forties) and sleeker with gadgets and superpowers. While Mary Sue commonly has a piece of jewellery or a talisman that gives her power Jack Stone has his gang of 'in the know' at his high tech lab. James Bond is a typical example as are Neo from The Matrix and the hard boiled detectives from crime noir.

The three traits that define the Mary Sue/Jack Stone are a) the protagonist will get away with things/behaviour other people can't (doesn't play by the rules) and b) they are the best in the story, those characters that don't like them are seen as almost sub-humanly horrible with no redeeming qualities.