Who is Ventus from KH BBS?

Ventus is one of the three protagonists/playable characters of Kingdom Hearts: Birth by Sleep.

Ventus was a former apprentice of Master Xehanort before moving in with Master Eraqus and his two apprentices, Terra and Aqua. While training under Master Xehanort, his heart was fractured and to survive he borrowed part of the light from Sora's heart (this is why Sora's Nobody, Roxas, looks exactly like Ventus).