Should I use an article or not? (Rotkäppchen oder das Rotkäppchen?) So first of all, english is also not my mother tongue. I am stating this because there is no articles in my mother tongue. Even "the" not exists. Even so, I believe that I  understood the logic behind articles, yet in some examples I just can't get it. 

I was doing a homework about early german fiction. I realized that, some people consider the nickname of the girl as a noun and writing as "Das Rotkäppchen" I know that "-chen" comes with "Das" and it is kind of a "reduction"  but isn't it a nickname? And there aren't millions of "Rotkäppchen"s in the world. This is not like "the apple or etc." When we say "Rotkäppchen" we know who she is... She is one and only Rotkäppchen. So... Which one is right? Isn't "Das Rotkäppchen" a wrong artcile usage? If not, why?