Members of the Church of the Silence, formerly the Papal Mainframe, the Confessional Priests (also known as Silents, Second Human Empire: Memory Thieves), were genetically engineered by the Church to allow people to confess their sins without remembering doing so, accomplished by fashioning the Priests so anyone looking at them would forget their encounter when they looked away (though, oddly enough, this doesn't seem to work on Transrace however). A renegade batch of Priests became obsessed with preventing the Siege of Trenzalore, and travelled back in time, influencing human history over a long period of time, and attempting to create a fixed death for the Doctor at Lake Silencio. They became known to the Doctor as Silents.