Quetzalcoatl was an Aztec god, and one of the four sons of the Lord and Lady of Our Duality.
Each son was called Tezcatlipoca, but differentiated by colour. Quetzalcoatl was the white Tezcatlipoca. He was white-skinned and bearded. According to legend, he was overthrown by the Black Tezcatlipoca and exiled across the ocean, but would return in the year One Reed. This coincided with the arrival of Fernando Cortés, who was mistaken for the returning deity. When the Seventh Doctor went to 1487 Tenochtitlan to track the Blue, some people there thought he might be Quetzalcoatl, though he lacked a beard. (PROSE: The Left-Handed Hummingbird)