Blake Belladonna

Black Black is one of the main characters in RWBY. She has yet to make an appearance.

Speculation
Note: The following is fan speculation, and is not to be considered canonical.

The lyrics in the song Red like Roses, along with Red's strong resemblance to Red Riding Hood, have led fans to believe that each of the main characters is inspired by a popular fairy tale. In Black's case this character may be Belle from Beauty and the Beast. She may also be a derivation of the Black Bride, from the Grimm tales. This is supported by the fact that the Black Bride is seen as a false hero, which can be viewed as a beast.

It is speculated that the weapon Black carries is that of a form of a whip, but it will be revealed when Blacks trailer is released, if she will have a trailer like Red does.