A satanist is a practitioner of satanism. Satanism, the cult of Satan, or Satan worship, is in part a survival of the ancient worship of demons and in part a revolt against Christianity or the church. It rose about the 12th century in Europe and reached its culmination in the blasphemous ritual of the Black Mass, a desecration of the Christian rite. The history of early Satanism is obscure. It was revived in the reign of Louis XIV in France and is still practiced by various groups throughout the world, particularly in the United States.
One of the largest and most influential Satanic groups is the Church of Satan (1966), founded by Anton LaVey in San Francisco. A splinter group, the Temple of Set (1975), was organized by Michael Aquino. Many Satanic groups, including the ones mentioned, attest that such worship does not necessarily imply evil intentions, but rather an alternative to the repressive morality of many other religious groups. Such groups see no harm in their indulgence in "worldly pleasures" that other religions forbid. However, they have not taken heed to Christ's warning in the gospel: For what does a man profit, if he should gain the whole world and suffer the loss of his soul? or what shall a man give in exchange for his soul?" (Matthew 16:26).
In terms of theology, Satanists today can be divided into two main groups:
atheistic Satanism does not believe that "Satan" actually exists, as such, they do not worship Satan. They believe every person is their own god and that everyone should worship themselves. To them, "Satan" is just a symbol of rebellion. The most well-known example of this group is Anton LaVey, founder of the Church of Satan.
theistic Satanism believes that "Satan" is an actual independently existing being, whom they worship and serve as their god.
Satanists differ in their attitude towards the God of the Bible. Atheistic Satanists deny that the God of the Bible exists. Theistic Satanists vary in their opinions:
some deny God's existence
some believe that God exists, but is weaker than Satan
some believe that God exists, and that Satan is weaker and God will ultimately triumph over him - and even, they will be consigned along with Satan to an eternity in hell. But, they believe, "Better to reign in Hell than serve in Heaven", as Milton said.
Another more sociological division of Satanists:
organized Satanism - these are organized, publicly known Satanic groups. They publicly oppose criminal activity, and have well-developed theologies which they often publish electronically or in printed form
dabbler Satanism - teenagers who turn to Satanism as a form of rebellion against their parents, school, church, etc. Generally they lack a well-developed theology. Often are involved in petty crimes such as vandalism, although occasionally have been linked to more serious criminal activity. Most of them grow out of their Satanism, although some will develop into another form of Satanism over time.
'sicko' Satanism - criminals, psychopathic individuals, that use Satanism as a justification for criminal activities such as murder, rape, child molestation, etc. Generally lack a developed theology. In some cases the trappings of Satanism are used to try to scare victims (especially children) into not coming forward. Most commonly are loners, or occasionally small groups
'showbiz' Satanism - musical and other groups who use the trappings of Satanism for artistic purposes. Sometimes this is meant seriously (e.g. the musician is an adherent of organized Satanism, and sees their art as a vehicle for spreading Satanic ideas.) In other cases, Satanism is not adopted as a belief system but rather chosen to be shocking or outrageous, or due to an artistic preference for 'dark' imagery
conspiratorial Satanism - large scale, conspiratorial groups which practice human sacrifice, child molestation, etc., many of whose members allegedly occupy positions of power, authority or respect in their communities, such as doctors, lawyers, politicians, police officers, schoolteachers, etc.
Satanism became a socially recognized phenomenon with the advent of The Satanic Bible (1969) and The Church of Satan.
The Satanic Bible contains the core philosophy of LaVey Satanism. the concepts were based on the philosophies of Nietzsche and "The Will to Power" and Ayn Rand "Atlas Shrugged". The Satanic Bible is the core document for many Satanists. The philosophy of LaVeyan Satanism is based on objectivism, humanism, and rationalism.
The majority of LaVey Satanists are atheist and they see Satan as a symbolic metaphor for life and nature. The method of Magic promoted by the Church of Satan is psychological and primarily non-esoteric. Most members of the Church of Satan do not accept the existence of an afterlife.
There are other groups which came from this social phenomenon created by LaVey. The initiatory organization known as the Temple of Set was created in 1975 by Lt. Colonel of the US Army Michael Aquino and other members of the Church of Satan who left after a disagreement in policy. The Temple of Set is a legally recognized non-profit church.
Independent Satanism is an eclectic form of Satanism that focuses on individualism and self enlightenment without the aide of group or organized Satanism. Many are self-initiated into the practice of Satanism and are known as solitary practitioners of magic. The method of independent Satanism include the signing of a pact or agreement with their chosen Satanic deity. Independent Satanism can take on a variety of beliefs from different sources, and they tend to develop their own personal life philosophy independent of popular Satanic thought.
Theistic Satanism is often classified as Satanic worship, the worship of the Christian Satan. While some practice this form of "Satanic Christianity", other Theistic Satanists choose to see Satan as one of many gods, and may not choose to include worship as a part of their personal spirituality. Theistic Satanists may practice a form of Satanic Henotheism, which is the dedication to Satan while including other gods into their personal pantheon.
"Christian Satanism", sometimes labeled as "Traditional Satanism", combines elements of Christianity with Satanic myth and religion. The Traditional Satanist philosophy may include the belief in Satan as a creator god (gnosticism), or Satan as the enemy of the Christian God. Traditional Satanists also tend to believe in the existence of the afterlife. Some Traditional Satanists use the Al-Jilwah as a religious document based on the belief that the Al-Jilwah is the revealed word of Satan.
Satanism is not easily summarized. How Satanism is defined depends on what "division" of Satanism you are referring to. In contrast to Christianity, Satanists themselves disagree on their very fundamental principles. While Christians may differ in opinion or conviction about interpretation of certain Bible passages not yet defined by the Church, Christians believe the same foundational principle that Jesus is God's Son who paid the price for our sins by dying on the cross and rising from the dead. Satanists in different camps argue whether there even is a Satan and whether they are worshiping him or themselves. In essence they are a confused lot bound by and to lies. John 8:44 is perhaps a good summary of Satanism: "You belong to your father the devil, and you want to carry out your father's desire. He was a murderer from the beginning, not holding to the truth, for there is no truth in him. When he lies, he speaks his native language, for he is a liar and the father of lies."
It is because of these lies that there is a plethora of ideologies and false philosophies in Satanism. You can be hard pressed to find a handful outside their own coven, church, or group that "believe" the same way. Some of Satanism's practices are constant, but Satanists' comfort and unity is found more in the "acts" of rituals than in the "relationship" to a belief system. It is easier to call themselves "Satanists" if they "do" certain things.
There is the Church of Satan, Satanists, Devil Worshippers, and many other categories included in Satanism. Most of them claim to have roots stemming from Anton LeVey, the author of the Satanic bible and founder of the first Church of Satan. (Side note: He presumably started the first Church of Satan in 1966. As a self-proclaimed authority on everything evil, he began giving weekly lectures at the cost of $2 per person. And thus the Church of Satan was born.
Even in their harsh disagreement of principles and beliefs, there is an underlying commonality: self. The very sin for which Satan was forever dismissed from God's presence is their common denominator: selfishness. All forms of Satanism claim that life exists to consume. Wicca demands you treat mother earth with respect and use the power that is within her and yourself, but for your own good. Devil worshippers hail allegiance to Satan and think he will guard them for all eternity; that is, if they believe there is an eternity. Some adherents of Satanism hold that the only existence they will ever know is here on earth. And thus, devil worshippers live for the moment and their creed is gluttony and debauchery.
Satanism gives its allegiance to Satan, while at the same time some in the Church of Satan believe no God or Satan truly exists. Most of the Church of Satan also believes that there is no redeemer for them or anyone else. Each person is fully responsible for the path of his own life. But then they turn around and pray to Satan in rituals, asking for his sovereign hand to be manifested in their lives. This kind of thinking is characteristic because of the influence of lies and deceptions throughout their philosophy. In light of this, some Satanists don't believe in the Satan of the Bible because he was a fallen angel—and who wants to follow a loser? The best lie Satan ever told was that he didn't exist, and his interest is in turning people away from Christ. Whether they believe in him or not is actually irrelevant to him, as long as the end result is the same—their souls in bondage to him in hell.
In short, Satanism, while it may or may not be worshiping Satan, is a conscious effort to NOT worship the one true real God. Romans 1 gives a clear look into the heart and motives of a Satanist. They have "depraved minds to do what ought not to be done. They have become filled with every kind of wickedness" (Romans 1:28-29). People who have been misled by Satan into this lifestyle have a hard time understanding God's concept of grace and freedom. Instead, they live for themselves, by themselves. Their identity is shaped by the events and seeming lofty ideologies of their contemporaries rather than in the truth of the ageless and forever true God.
Second Peter 2 contains a warning to anyone who would follow after Satanism or any other thing rather than God: "These are fountains without water, and clouds tossed with whirlwinds, to whom the mist of darkness is reserved. For, speaking proud words of vanity, they allure by the desires of fleshly riotousness, those who for a little while escape, such as converse in error: Promising them liberty, whereas they themselves are the slaves of corruption. For by whom a man is overcome, of the same also he is the slave." (2 Peter 2:17-19).