The Brethren are a 16th century Christian group of corrupt monks led by Father Angelo and they one of the many antagonists in the Doctor Who series. They first appeared alongside their leader in the episode "Tooth and Claw". The members of this sinister cult which is originated in the European country of Scotland, could be recognized by their bald heads and orange or black robes.
The Brethren used an unknown type of martial arts, though they weren't above shooting people. They might also have trained the Werewolf to fear mistletoe.
Some time in the 1540s, the Brethren discovered the Lupine Wavelength Haemovariform's crashed spaceship and decided to try to help it. They turned away from their God and started to worship the Wolf. They provided hosts and food for the growing werewolf for over 300 years.
In 1879, they also arranged events for Queen Victoria to be bitten to start "The Empire of the Wolf". This plot was foiled by the Tenth Doctor and Rose Tyler, and both Father Angelo and the Wolf were killed. It is unknown what happened to the rest of the Brethren but it is cleared the cult were certainly disbanded and killed in the end.