Catharism had its roots in the Paulician movement in Armenia and eastern Byzantine Anatolia and the Bogomils of the First Bulgarian Empire, who were influenced by the Paulicians resettled in Thrace (Philipopolis) by the Byzantines. Though the term "Cathar" (/ˈkæθɑːr/) has been used for centuries to identify the movement, whether the movement identified itself with this name is debatable. In Cathar texts, the terms "Good Men" (Bons Hommes) or "Good Christians" are the common terms of self-identification. The idea of two Gods or principles, one being good and the other evil, was central to Cathar beliefs. The good God was the God of the New Testament and the creator of the spiritual realm, contrasted with the evil Old Testament God—the creator of the physical world whom many Cathars, and particularly their persecutors, identified as Satan. All visible matter, including the human body, was created by this evil god; it was therefore tainted with sin. This was the antithesis to the monotheistic Catholic Church, whose fundamental principle was that there was only one God, who created all things visible and invisible. Cathars thought human spirits were the genderless spirits of angels trapped within the physical creation of the evil god, cursed to be reincarnated until the Cathar faithful achieved salvation through a ritual called the consolamentum.
From the beginning of his reign, Pope Innocent III attempted to end Catharism by sending missionaries and by persuading the local authorities to act against them. In 1208 Innocent's papal legate Pierre de Castelnau was murdered while returning to Rome after excommunicating Count Raymond VI of Toulouse, who, in his view, was too lenient with the Cathars. Pope Innocent III then abandoned the option of sending Catholic missionaries and jurists, declared Pierre de Castelnau a martyr and launched the Albigensian Crusade.