Satan is the devil and guardian of Hell. He does make some appearances in Pearls. Satan is a conniving, con artist who can trick people into going into hell. He was shown to be nice in the beginning, since he was Rat's friend (no surprise there). He then went back to evil and tricked two crocs into going to Hell.
Satan is a friend of Rat because they both have the same personalities, and both are evil.
Satan tricks numerous people into going to Hell and tortures them.