Christianity

Christianity was one of the major religions of Earth. It centred around the teachings of the religious figure Jesus Christ, who was born in (approximately) 4 BC. Humans would come to base their calendar for much of their history on the estimated year of Christ's birth. The Doctor was apparently present at his birth (DW: Voyage of the Damned) and his death/resurrection (DW: Planet of the Dead). These two events were responsible for the Earth holidays of Christmas and Easter, respectively. Christianity was one of countless religions throughout the universe to have a devil figure inspired by 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)

One Time Lord assumed the persona of a Monk in order to alter history in 1066 England. (DW: The Time Meddler)

Christian leaders fought a series of Crusades in the 12th and 13th century, in which the Doctor and his companions became involved. (DW: The Crusade)

In the 16th century, Christianity split into two groups: the main group, which had become known as the Catholic Church; and the splinter group, who called themselves Protestants. The two groups came into conflict on several occasions, one notable example being the St. Bartholomew's Day Massacre. A key figure in the events leading up to this massacre was the Abbot of Amboise, who bore a striking resemblance to the Doctor. (DW: The Massacre of St Bartholomew's Eve)

A group of Christian monks in Scotland were turned away from their religion, instead harbouring and worshiping a Lupine Wavelength Haemovariform which had crashed there. (DW: Tooth and Claw)

The Master masqueraded as a Christian priest as part of his plan to summon Azal. (DW: The Dæmons)

The Gorgon was harboured by an order of Christian nuns for generations. (SJA: Eye of the Gorgon)