Qrow Branwen

Qrow (pronounced "Crow") is a currently unseen (in person) character in RWBY, and the uncle of Ruby Rose and Yang Xiao Long. He is a teacher at Signal Academy. He was mentioned in "Ruby Rose" as being the one who taught Ruby how to fight and wield her High-Caliber Sniper-Scythe, Crescent Rose.

Ozpin revealed their acquaintance when he deduced that Qrow was the source of Ruby's talent with such an uncommon weapon, as he knows of no other scythe-wielders of such comparable skill.

At the end of "Black and White," Ozpin, while viewing footage of the aftermath of the battle, receives a cryptic message from Qrow: "Queen has pawns." James Ironwood also knows Qrow and has been in contact with him.

It is revealed in "Burning the Candle" that Qrow was on a team with Ruby and Yang's father, Taiyang Xiao Long, as well as Summer Rose and Yang's Mother.

Abilities
As mentioned by Ozpin, Qrow is a master scythe wielder, having taught Ruby how to use her scythe. Qrow's scythe is confirmed not to be Crescent Rose, as Ruby stated that she made Crescent Rose herself. In Yang's flashback he was shown easily dispatching three Beowolves single-handed, showing that he has remarkable skill of his weapon.

Trivia

 * The mumbling of the phrase "That's my uncle!" by Ruby is a reference to the Rooster Teeth Animated Adventure Left 4 Trek.
 * Qrow was first seen in "Burning the Candle," not in a rendered model, but only as stylized artwork.