Eraqus

Eraqus is the teacher and caregiver of Terra, Aqua and Ventus, and a Keyblade Master. Eraqus is very wise, noble and righteous, and stands strongly on the side of light, believing that darkness is pure evil and must be eliminated. This belief eventually causes him to turn his keyblade on Ventus and later on Terra after learning what Xehanort’s true intentions were for Ventus. Eraqus trained under the same master as Xehanort, and when the two were younger they were extremely close; from the looks of it, they were like brothers. Eraqus has only appeared in Kingdom Hearts Birth by Sleep and Birth by Sleep Final Mix. However, it has been heavily implied that we will be seeing a younger version of Eraqus in Kingdom Hearts III.