An idol worshipped at Ekron
The earliest biblical appearance of the name is in the story of Ahaziah, king of Israel. After a serious fall, Ahaziah sent messengers to ask Baal-zebub, the god of Ekron, whether he would recover. Ekron was a Philistine city, not a place where Israel's king should have sought spiritual help (2 Kings 1:2).
Elijah confronted this choice sharply. He asked whether there was no God in Israel, since Ahaziah had turned to a foreign god instead (2 Kings 1:3). The story is not mainly interested in describing this idol's origin or appearance. Its concern is Ahaziah's refusal to seek the Lord.
But the angel of the Lord said to Elijah the Tishbite, Arise, go up to meet the messengers of the king of Samaria, and say unto them, Is it not because there is not a God in Israel, that ye go to enquire of Baal–zebub the god of Ekron?
Why the name changes
In the New Testament, the name is usually written Beelzebub. The spelling and meaning have been discussed for centuries. Baal-zebub in 2 Kings is often understood as meaning something like “lord of flies”, while Beelzebub may reflect a related form of the name. The Bible itself does not pause to explain the linguistic history, so it is wise not to build too much on one proposed meaning.
What is clear is how the name functioned in Jesus' time. It referred to the chief or prince of demons, not simply to an old Philistine idol. In that setting, Beelzebub became a title associated with the power of evil.
An accusation against Jesus
When Jesus healed a man oppressed by a demon, some religious leaders claimed that he cast out demons by Beelzebub, whom they called the prince of devils (Matthew 12:22-24). It was a serious accusation. Rather than denying that the kingdom of darkness exists, Jesus exposed how little sense their claim made.
If Satan were using Jesus to drive out Satan's own demons, Jesus said, Satan's kingdom would be divided and could not stand (Matthew 12:25-26). Jesus' works showed the opposite: God's reign was breaking into people's lives and setting them free from evil's grip (Matthew 12:28).
But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you.
Beelzebub and Satan
The New Testament does not give a separate biography of Beelzebub or present him as a different good or neutral spiritual figure. In Jesus' teaching, the name belongs on the side of Satan and demonic opposition to God's work. Luke records the same charge and Jesus' same answer about a divided kingdom (Luke 11:15-18).
So, who was Beelzebub? In the Old Testament background, the name belonged to Ekron's false god. In the New Testament, it was a name for the ruler of demons, identified with Satan's kingdom. The point of these passages is not to satisfy curiosity about every detail of the unseen world. It is to show that Jesus has greater authority than the powers that harm and deceive.