Historically, one of the most important protagonists of the movement was Walter Martin (1928-89), whose numerous books include the 1955 The Rise of the Cults: An Introductory Guide to the Non-Christian Cults and the 1965 The Kingdom of the Cults: An Analysis of Major Cult Systems in the Present Christian Era, which continues to be influential. He became well known in conservative Christian circles through a radio program, "The Bible Answer Man", currently hosted by Hank Hanegraaff.
In The Rise of the Cults Martin gave the following definition of a cult:
By cultism we mean the adherence to doctrines which are pointedly contradictory to orthodox Christianity and which yet claim the distinction of either tracing their origin to orthodox sources or of being in essential harmony with those sources. Cultism, in short, is any major deviation from orthodox Christianity relative to the cardinal doctrines of the Christian faith.
As Martin's definition suggests, the countercult ministries concentrate on non-traditional groups that claim to be Christian, so chief targets have been The Church of Jesus Christ of Latter-day Saints, Jehovah's Witnesses, Christian Science and the Unification Church, but also smaller groups like the Swedenborgian Church
Various other conservative Christian leaders-among them John Ankerberg and Norman Geisler-have emphasized themes similar to Martin's. Perhaps more importantly, numerous other well-known conservative Christian leaders as well as many conservative pastors have accepted Martin's definition of a cult as well as his understanding of the groups to which he gave that label. Dave Breese summed up this kind of definition in these words:
A cult is a religious perversion. It is a belief and practice in the world of religion which calls for devotion to a religious view or leader centered in false doctrine. It is an organized heresy. It is perverted and lies.