Ha-Satan (meaning "the Devil" in Hebrew) is a figure found in the writings of the Abrahamic religions. Muslims, Christians and Jews believe that he tempts people to do bad things. His role is to question and tempt people's faith. Christians also say that he was once an angel named Lucifer. Some Muslims on the other hand believe, he was once an angel called Azazel.
In Satanism, Satan is thought to be just a metaphor for what humans want. In Theistic Satanism, Satan is considered to be a good force.