Beelzebub is one of the seven princes of the underworld, or hell. The name is derived from the Hebrew Ba'alZebub, which translates as "Lord of the Flies". The deity is semitic in origin, and is believed to have been worshipped by the Philistine inhabitants of the ancient city of Ekron.
In the Testament of Solomon, Beelzebal is referred to as the Prince of Demons. He spreads chaos and destruction upon the earth through evil tyrants, and he will trick men into worshipping demons and false gods.
In Christianity, especially Catholicism, Beelzebub and Satan are considered one and the same.