The Red Guardian was part of the Six-Fold God of the Six-Fold-Realm and a Guardian of Time that represented Justice. (PDA: The Quantum Archangel)
According to an apocryphal account, the Red Guardian of Justice was originally the thirteenth incarnation of the Doctor, and the Beige Guardian was jealous of the fact that he had the name Red Guardian, while he was stuck with Beige Guardian. (CP: Aspects of Evil (Missing Pieces))