Bogomil was a 10th-century Bulgarian priest and heresiarch

Heresiarch

A heresiarch is a founder or leader of a heretical doctrine or movement, as considered by those who claim to maintain an orthodox religious tradition or doctrine...

, who was connected with the origins of Bogomilism

Bogomilism

Bogomilism was a Gnostic religiopolitical sect founded in the First Bulgarian Empire by the priest Bogomil during the reign of Tsar Petar I in the 10th century...

. According to Cosmas the Priest

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 priest Bogomil first began to preach his heresy in Bulgaria in the reign of the Peter I of Bulgaria

Peter I of Bulgaria

Peter I was emperor of Bulgaria from 27 May 927 to 969.-Early reign:Peter I was the son of Simeon I of Bulgaria by his second marriage to Maria Sursuvul, the sister of George Sursuvul. Peter had been born early in the 10th century, but it appears that his maternal uncle was very influential at...

 (927 to 969), which indicates that Cosmas must have been writing later than 969. As with Cosmas the life of Bogomil is shrouded in mists and what little we know of him comes from the sermons written against him. There is some uncertainty about his relationship to Jeremiah

Jeremiah (Bulgarian priest)

Jeremiah was a 10th-century Bulgarian priest and writer usually associated with the origins of Bogomilism.He is mentioned for the first time in the tenth century by Patriarch Sisinnius II of Constantinople c. 996–999...

or whether they are the same person. The statement that Jeremiah was "a son (disciple) of Bogomil" may be an interpolation.