A heretic is a person who holds a belief or theory that is strongly at variance with established beliefs or customs, particularly the accepted beliefs or religious law of a religious organization. The term "heresy" is usually used within a Christian, Jewish, or Islamic context, and implies slightly different meanings in each. The founder or leader of a heretical movement is called a heresiarch, while individuals who espouse heresy or commit heresy are known as heretics.
Historically, the Christian church dealt with many heresies, and the church regarded itself as the custodian of a divinely imparted revelation which it alone was authorized to expound under the inspiration of the Holy Spirit. Thus, any interpretation that differed from the official one was necessarily "heretical" in the new, pejorative sense of the word.
The term "heretic" is almost always pejorative and means someone who has forsaken a religion or is speaking out against the one true religious doctrine. It is someone who goes against the official teachings of the Church, so from the point of view of the Church, usually the Catholic Church, it is a negative thing.
