Anyone who has been reading or writing fanfiction has likely heard of the name 'Mary Sue'. Mary Sue isn't a person, just the general (and derogatory) name for an original female character who either lacks good characterization OR who is an avatar for blatant author wish fufillment (or both for that matter). The male version is Gary Stu, but he's unlikely to show up in Bieber fics, so we'll shove him aside for now.
Not every original character is a Mary Sue and not every character with Mary Sue-like traits is a Mary Sue. That said, it is wise to take note of the major characteristics of Mary Sue and judge your potential OCs.Potential Mary Sue Flags1. Unusual physical features just for the sake of being unusual.
Forget the flag, this is a blaring Mary Sue klaxon. There can be justification for unusual features (supernatural elements, being part of a subculture, etc.) but if Destiny Crystal Skychilde has violet eyes just because you thought it would be awesome if you had them, you're heading towards a Sue. Now if your character has violet contact lenses in because she is ignored by her family and is cultivating a strange appearance because she is seeking attention elsewhere, that's another issue. Speaking of Destiny Crystal Skychilde...2. 'Cool' names, your name, or the one you wish you had.
Just having a nifty name is not a problem, but it can be a warning flag for wish fulfillment territory. This also includes foreign names for non-foreign characters (ex. Sakura for a mid-western white girl) and having multiple first or middle names for no apparent reason.3. Your character is obscenely beautiful.
Just like the first two flags, this one isn't necessarily a huge deal. However if your character is just drop dead gorgeous AND she's got violet eyes and that cool tattoo you've always wanted AND she's got an Awesome McCoolname
name...3b. Your character is obscenely beautiful but you've given her a 'flaw' that really isn't a flaw.
This is usually the result of an author realizing that things are looking Sue-ish and trying to backpedal. Having an obvious birthmark, too full lips, etc. aren't really going to detract from her beauty.3c. Constantly describing your character.
If you're always describing your characters 'violet orbs' or constantly mentioning how beautiful she is, you're on a slippery slope. This goes double if you don't dote on other characters' physical appearances.4. Your character is great at EVERYTHING.
People aren't great at everything they've ever tried. The term 'jack-of-all-trades' exists because some people are okay with most things they try, but there's a reason the rest of the saying is 'jack of all trades, master of none'. If Destiny can outsing Justin, outdance the backup dancers, handle business better than his manager, cook better than a chef, give a better massage than a therapist, and just happens to know 5 forms of martial arts just so she can save Justin's ass from a mugger, she's probably a Mary Sue. That's not to say that a character can't be an expert in a thing or two, just remember that you don't find my many doctors who are also professional chefs and olympic athletes.5. Your character has no believable flaws.No one is perfect.
Believable characters have personality and other flaws that they need to overcome. The real key is to make them realistic. Not being able to sing is not a good flaw. Not being able to sing but being narcissistic enough to think you sing like angel, is. These flaws must also affect the story. If your character is hotheaded but it doesn't cause a conflict with other characters the flaw won't come off as relevant or realistic.6. A horribly tragic backstory that doesn't seem to have really affected your character.
It was terribly tragic that Destiny's parents were brutally murdered in front of her before the baddies kidnapped her little brother, raped her and ran over her dog, but if that hasn't really affected her in some way, than she probably doesn't need the tragic backstory. Occasionally angsting so Justin can comfort her isn't the same as a realistic affect. We are shaped by our past experiences and a character who was mugged might be fearful to go out at night by herself, a character who lost her parents at a young age might be unwilling to form emotional bonds with people, a character with an abusive ex might not want to be in a relationship, etc.7. Your character makes other people behave strangely.
This is usually a problem with wish-fufillment Sues. In order to clear the way for Destiny to get in Justin's pants, the author might turn his girlfriend into a violent, angry, cheating asshole without giving any sort of explanation for the characterization. His friends might turn into instant Destiny/Justin shippers and not mind that he's spending 24/7 with her and ignoring them. 7b. Everyone in the story likes your character (except for characters you personally don't like)
Exactly what it says on the tin. If animals and small children also like your character, it's time to stop typing and re-think things.
Again, having some of these flags doesn't necessarily mean you're writing a terrible character. Mary Sue's can be turned into viable characters by giving them some realistic problems, flaws and issues to deal with.