Baalzebub, &, is one of the demon princes who appears in Gehennom. He will be found in his lair, if you do not encounter him earlier. He is quite easy to defeat, though many consider him annoying because of his repeated use of a stunning gaze. Blindfold yourself and fight him on the up staircase; Elbereth is usually not necessary.
Yet another Dungeons and Dragons monster. D&D actually uses the spelling "Baalzebul".
The encyclopedia entry comes from the novel Lord of the Flies. As the entry says, Baalzebub is a confused Bible term, translated as "lord of the flies", from which the famous novel takes its title. In Christian demonology he is described as a demonic fly.
The D&D Baalzebul appears as a giant slug-like creature which trails feces and garbage wherever he goes. Flies crawl over his body at all times, and his arms are tiny and malformed.
You may find representations of him as a dark-skinned humanoid with compound insect eyes. According to D&D, he initially looked like that, but later he was punished by Asmodeus into his current form.
The "lord of the flies" is a translation of the Hebrew Ba'alzevuv (Beelzebub in Greek). It has been suggested that it was a mistranslation of a mistransliterated word which gave us this pungent and suggestive name of the Devil, a devil whose name suggests that he is devoted to decay, destruction, demoralization, hysteria and panic...