Cosmas the Priest

Cosmas the Priest, also known as Cosmas the Presbyter or Presbyter Cosmas, was a medieval Bulgarian priest and writer. Cosmas is most famous for his anti-Bogomil treatise Sermon Against the Heretics, which, despite not being conclusively dated, is generally ascribed to the 10th century. The treatise is a valuable source on the beginnings of the Bogomil heresy in Bulgaria, as well as on medieval Bulgarian society.