According to Christianity, Satan is the epitome and embodiment of all evil things, described as "the father of all lies" in the Catholic Church's Catechism (paragraph 391). It is his works that tempt humans into doing bad deeds. If something evil occurs, we can be assured that Satan had something to do with it.
The History of Satan
According to Catholicism, Satan only exists because God allows him to (The Catechism of the Catholic Church, paragraph 395). This raises some serious issues about how righteous God can be if he allows evil to exist, but I digress. Satan, as the story goes, began as the angel Lucifer, who outrightly rejected God and rebelled against him. God cast Lucifer and those who followed him into Hell, a place of eternal torture and despair, where God was not present.
Like any good propoganda machine, Christian authorities have made sure to limit the disenimation of information on the enemy (Satan) to what they want the public to know. For example, we are never told why Satan rebelled against God. We're never given his side of the story. Were Satan's reasons for rejecting God and attempting to overthrow him legitimate? From where I'm standing, they could certainly be considered valid if the authorities see fit to hide them from the general public.
For example, the Catechism of the Catholic Church, the book that outlines Catholic beliefs in detail, has barely half a column in its index devoted to Satan and information on him, where as Jesus Christ has a full 6 pages! Sound like a propoganda machine to you, yet?
Christian authorities have made some big mistakes with their anti-Satan propoganda machine, however. Since there is so little information available about Satan, there is no record of anything he's done or any way to connect events to him. Christians simply and lazily accredit evil occurences to Satan. A good example are the events of September 11. Within weeks, a doctored picture was floating around the internet showing Satan's face in the clouds of smoke and debris eminating from the two towers, thus unfairly making Satan out to be responsible for these tragedies.
Satan vs. God
The only evidence we have to conclude Satan's utter evil is God's word, and frankly, God's word isn't worth too much. He's shown a remarkable inconsistency in his actions and words, and he's hardly above lying or dishonest conduct. Straight after giving Moses the first set of Ten Commandments (which included "Thou shalt not kill"), he let Moses go ahead and order the Levites to go on a mass-murdering rampages, which they did, but only after he talked God out of killing all the people! According to 2 Thessolonians 2:11-12, God will send a strong illusion to people so that they will believe lies, so he can condemn everyone to Hell. After giving Moses the Ten Commandments, God orchestrated a litany of atrocities through isoltated commandments that are simply too great in number to list here. I suggest checking out the The Skeptic's Annotated Bible to see for yourself, specifically this section. These events are detailed in Exodus 32. In 2 Chronicles 18:22, God lies to prophets. Why should anyone take his word at face value if he has no problem with lying to us for no reason other than to have an excuse to condemn us to Hell?
Who's more evil? God or Satan? How can we determine this? Well, it's a simple matter of looking at the actions of both God and Satan. Who's commited more evil acts? Who's done more harm to humanity? Who's been the most oppressive? Is Satan really as bad as the Christian Smear Campaign makes him out to be? Let's find out...