Beelzebub's name means "lord of the flies," and this second-in-command to the devil is the most competent of the swarm of vicious demons that surround Satan in hell. He is a loyal sycophant who is both swayed by Satan's charismatic and commanding presence and willing to flatter him, saying,
Leader of those Armies bright,
Which but th' Onmipotent none could have foyld [foiled] . . .
Satan doesn't need Beelzebub's praise to believe he is the greatest of beings, and he is probably a bit annoyed that Beelzebub's flattery puts him second to God. Nevertheless, Beezlebub does support Satan's schemes for upsetting God's most cherished plans.
Like a good propagandist, Beezlebub is able to present a somewhat smooth and commanding front that masks his inner darkness, and he is able to employ his persuasive powers to sway the other demons to follow Satan's lead.
He is an evil character who willingly participates in spreading misery and thwarting (he thinks) God's plans, but he also accepts that he is second to Satan, showing he does not have Satan's overwhelming pride.