Beelzebub (more accurately Ba‘al Zebûb or Ba‘al Zəbûb), appears as the name of a god worshipped in the Philistine city of Ekron. It is later the name of a demon/devil, often interchanged with Beelzebul. In Christian writings, either form may appear as an alternate name for Satan or the Devil or may appear as the name of a lesser devil.
The only early source for the name Ba‘al Zebûb / Beelzebub is in 2 Kings 1.2–3,6,16 where King Ahaziah of Israel, after seriously injuring himself in a fall, sends messengers to inquire of Ba‘al Zebûb, the god of the Philistine city of Ekron, to learn if he will recover. Elijah the Prophet then condemns Ahaziah to die by Yahweh's words because Ahaziah sought council from Ba‘al Zebûb rather than from Yahweh.
Ba‘al Zebûb might mean 'Lord of Zebûb', referring to an unknown place name Zebûb, or 'Lord of flies', zebûb being a Hebrew collective noun meaning 'flies'. Cheyne suggested that it might be a corruption of Ba'al Zebul, 'Lord of the High Place'. The SeptuagintA renders the name as Baalzeboub, SeptuagintB as Baal myîan 'Baal of flies', but Symmachus the Ebionite may have reflected a tradition of its offensive ancient name when he rendered it as Beelzeboul (Catholic Encyclopedia).
In Mark 3.22, the Pharisees accuse Jesus of driving out demons by the power of Beelzeboul prince of demons, the name also appearing in the expanded version in Matthew 12.24,27 and Luke 11.15,18–19. The name also occurs in Matthew 10.25. It is unknown whether Symmachus was correct in identifying these names or not since we otherwise know nothing about either of them. Zeboul might derive from a slurred pronunciation of zebûb; from 'zebel', a word used to mean 'dung' in the Targums; or from Hebrew zebûl found in 1 Kings 8.13 in the phrase bêt-zebûl 'lofty house' and used in Rabbinical writings to mean 'house' or 'temple' and also as the name for the fourth heaven.
In summary, either or both of these names might be the a genuine divine title, or might be a corruption of such a title, possibly a purposeful corruption to make a mockery of it. The two names might refer to the same original or might not.
In any case the form Beelzebub was substituted for Belzebul in the Syriac translation and Latin Vulgate translation of the gospels and this substitution was repeated in the King James Version of the Bible, the result of which is the form Beelzebul was mostly unknown to western European and descendant cultures until some more recent translations restored it.
See also Baal.
In the Testament of Solomon, Beelzebul (not Beelzebub) appears as prince of the demons and says (6.2) that he was formerly a leading heavenly angel who was (6.7) associated with the star Hesperus (which is the normal Greek name for the planet Venus as evening star). Seemingly Beelzebul is here simply Satan/Lucifer. Beelzebul claims to cause destruction through tyrants, to cause demons to be worshipped among men, to excite priests to lust, to cause jealousies in cities and murders, and to bring on war.
Texts of the Acts of Pilate (also known as the Gospel of Nicodemus) vary in whether they use Beelzebul or Beezebub. The name is used by Hades as a secondary name for Satan.
Beelzebub is commonly described as placed high in Hell's hierarchy. According to the renowned 16th century occultist Johannes Wierus, Beelzebub is the chief lieutenant of Lucifer, the emperor of Hell, and presides over the Order of the Fly . Similarly, the 17th century exorcist Sebastian Michaelis , in his Admirable History (1612), placed Beelzebub among the three most prominent fallen angels, the other two being Lucifer and Leviathan, whereas two 18th century works identified an unholy trinity consisting of Beelzebub, Lucifer, and Astaroth. However, John Milton featured Beelzebub as merely being one of the many fallen cherubim in the epic poem Paradise Lost, first published in 1667. Beelzebub is also a character in John Bunyan's The Pilgrim's Progress, first published in 1678.
Sebastien Michaelis associated Beelzebub with the deadly sin of pride. However, according to Peter Binsfeld, Beelzebub was the demon of gluttony, one of the other seven deadly sins, whereas Francis Barrett asserted that Beelzebub was the prince of false gods. In any event, Beelzebub was frequently named as an object of supplication by confessed witches. After being accused by the Pharisees of possessing Jesus, he has also been held responsible for at least one famous case of alleged demon possession which occurred in Aix-en-Provence in 1611 involving a nun by the name of Sister Madeleine de Demandolx de la Palud who named one Father Jean-Baptiste Gaufridi as a bewitcher of young nuns. Beelzebub was also imagined to be sowing his influence in Salem, Massachusetts: his name came up repeatedly during the Salem witch trials, the last large-scale public expression of witch hysteria, and afterwards Rev. Cotton Mather wrote a pamphlet entitled Of Beelzebub and his Plot.
The title of William Golding's novel Lord of the Flies is a literal English translation of "Beelzebub".
Gurdjieff's magnum-opus 'All and Everything' 1st Series has a redeemed Beelzebub as the main character Beelzebub’s Tales to His Grandson