Satan is a term that traditionally describes an angel in Judeo-Christian believe and to a "jinn" in Islamic beliefs. This entity (the devil) is commonly referred to by a variety of other names, including Asmodai, Beelzebub, Lucifer and/or Mephistopheles. In classic demonology, however, each of these alternate names refers to a specific supernatural entity, and there is significant disagreement as to whether any of these specific entities is actually evil.
In the tradition of the Christian Church, Lucifer was an archangel, who had God's favor as the first angel among equals, but because of his vanity, hubris and weakness of character fell so far from God's grace that he was literally cast out of Heaven when he led other angels in revolt.
In art and literature, Satan has been depicted in numerous ways throughout history. According to one interpretation of the book of Genesis, Satan is identified as the serpent who convinced Eve to eat the forbidden fruit; thus, Satan has often been depicted as a serpent. (However, some care to argue that Lilith was the one who persuaded Eve to take this act upon herself.) This interpretation goes back at least as far as the time of the writing of the book of Revelation, which specifically identifies Satan as being the serpent (Rev. 20:2). In truth, Genesis makes no direct reference to the serpent having another identity, Satan or any other. It has been postulated by many Biblical scholars that Eden's snake is just a snake, able to speak, reason, and tempt Eve because it serves the explanatory purpose.
Satan tattoos are very similar to common demon tattoos. They represent vice, sin and temptation.