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)
Behind the Scenes
"Aspects of Evil" by Craig Hinton in the non-canonical Missing Pieces charity anthology states that the Red Guardian of Justice was originally the thirteenth incarnation of the Doctor and that the Beige Guardian was jelous of the fact that he had the name Red Guardian, while he was stuck with Beige Guardian.