Character in Buffy the Vampire Slayer. Introduced at the start of Season 5, aged 15. Buffy's sister. Say What?! Yes, it sounds like a glaring continuity error, and the show plays with the viewer, pretending for a while that all is normal. I'd include spoilers about her origin, but that would ruin it.

I have a suspicion that the reason why the character was introduced is that American TV executives believe that children won't watch TV unless there are young characters that they can relate to (This is the reason that Batman: The Animated Series was specially ruined by the introduction of Robin). The character is, however, a force for good: it allows the series to once again deal with such issues as burgeoning youthful sexuality, sibling relationships (Which it never has before), and for a more mature audience deal with parenting, and parental breakup. This latter happens in series 6, when Tara and Willow have to take over as Dawn's parents. If I'm right, it shows what kind of audience the showing is shooting for: everyone from the age of 13 to 30.

The character herself is often annoying, but occasionally sexy - More on this later. Dawn is mostly annoying because of her need for attention. She needs it so much, in fact, that in series 6 she becomes the classic problem child whose parents don't give her any attention. It may not be her fault, but it still annoys people. So much so, in fact, that at the end of series 6, Willow (Admittedly, in a less-than-chirpy mood) says, "Little, annoying Dawn. Always whining. Perhaps it would be better if you went back to being a ball of energy". Or something a lot like that.

Dawn is played by a very pretty girl. Dawn dresses like Buffy: In clothes that seem out of place on a girl less than 23 years old. (This is in no way to say that either dresses like a ho'.) This despite being Fifteen years old, and played by a sixteen year old (Information correct at time of going to press). So, she looks older than she is. In series 6, she also starts getting interested in vampires, err, boys. I predict more such story lines in series 7.