The Silent

Members of the Church of the Silence, formerly the Papal Mainframe, the Confessional Priests (also known as Silence), 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. 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.

_{Biography from the TARDIS Data Core article, licensed under CC-BY-SA}