Christianity

Christianity was one of the major religions of Earth. It centres around the teachings of the religious figure Jesus christ who was born in the year 1AD. The Doctor was apparently present at his birth (DW: Voyage of the Damned) and his death (DW: Planet of the Dead). These two events are responsible for the earth holidays of Christmas and Easter. Christianity is one of countless religions throughout the universe to have a devil figure inspired as the Beast. (DW: The Impossible Planet/The Satan Pit)

The Doctor met some early Christians while visiting Byzantium in 64. (PDA: Byzantium!)

When Christian missionaries tried and failed to exorcise Saul, they built a church on the site, then declared him an angel. (NA: Timewyrm: Revelation)

The Doctor and companion Amy Pond met a small squadron of priests led by Father Octavian, and are assumed to be Christians due to their names (Father, Cleric, etc,.). (DW: Time of Angels-Flesh and Stone)