Satan and Beelzebub are alike in both being evil and opposed to God. They both want to continue the fight against him, and both are underhanded and fiendish.
A main difference, however, is that while Satan is so proud that he will bow to nobody, Beelzebub, at least around Satan, is a sycophant and toady who kisses Satan's butt. For example, as they both come to life (the first two to do so) in the "mournful gloom" of hell, Satan springs up, assesses their horrible surroundings, and almost immediately decides it is better to rule in hell than serve in heaven. Among his first thoughts emerges the idea that wherever he lands, he will be in charge. It doesn't matter much to Satan that he is in hell as long as he can rule in hell.
Beelzebub, on the other hand, immediately begins flattering and fawning on Satan, saying to him of his fallen fellow angels in the fiery lake that when they see Satan:
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