Beelzeboul (Βεελζεβούλ) is a name applied to the prince of demons, identified with Satan. The name derives from the Hebrew Ba'al Zebub (בַּעַל זְבוּב, "lord of flies," 2 Kings 1:2–3) — the Philistine god of Ekron. By New Testament times the name had become a title for Satan himself as ruler of evil spirits. Jesus' opponents accused Him of casting out demons by Beelzebul's power (Matthew 12:24).
Jesus' response to the Beelzebul accusation (Matthew 12:24–32) is one of His most powerful theological statements about the kingdom of God's advance against Satan's kingdom: "If it is by the Spirit of God that I drive out demons, then the kingdom of God has come upon you" (Matthew 12:28). This passage also contains the solemn warning about blasphemy against the Holy Spirit. The accusation that Jesus worked by Beelzebul's power was to attribute the Holy Spirit's work to Satan — a fundamental confusion of good and evil that constitutes spiritual blindness at its deepest level.