The Red Guardian was one of the Six-Fold Gods of the Six-Fold-Realm and a Guardian Of Time that represented Justice. (PDA: The Quantum Archangel)
References
One source states that the Red Guardian of Justice was orginally the thirteenth incarnation of the Doctor. (Missing Pieces)
The Beige Guardian was jelous of the fact that he had the name Red Guardian, while he was stuck with Beige Guardian.