Baalzebul is one of the middle crop of infernal dukes. Back in the day, Baalzebul was known as the archon Triel. Triel was a very selfish perfectionist who kept wanting more and more out of his existence, which eventually caused his fall from grace. After being welcomed into hell, Triel rose through the ranks and attained the title of the Lord of the Flies, supposedly because his webs of intrigue were so tight that not even a fly could slip past him, though many pointed to the archduke's multifaceted, fly-like eyes.
Baalzebul eventually made his way to the rank of archduke and partook in the rebellion against Asmodeus. He was defeated but, though clever maneuvering, managed to hold onto his lordship anyway. All the same Asmodeus had his revenge and cursed him such that Baalzebul instantly had to spend a year in the form of that hideous slug-like form over on the right every time he lied to another devil... including all the lies he told before that curse was placed, meaning he had to go through a several-thousand-year span of being in this state and only recently was able to return to his true form again. But while in this form, Baalzebul is easily the most grotesque and disgusting of all the archdukes. Presumably it is his own ego that prevents such a clever bastard as him from exploiting the loophole in this curse, a loophole which surely would be obvious to any devil worth their salt: the curse is completely useless as a lie detector if he lies to someone while already in slug form. (He's probably vain enough to value having his true form over having the abillity to lie to other devils.)
To this day Baalzebul craves the downfall of Asmodeus as revenge for this humiliation. Thus far, he's had little success with this plan, but the Lord of the Flies has established a notable cultist presence on the Material Plane through a combination of lies, charm and promises of power. Aside from Asmodeus, Baalzebul despises Mephistopheles, who was one of his opponents during the rebellion in Hell. He counts Belial as an ally, but his daughter and co-ruler's relationship with Glasya and her growing power base makes this alliance at best unreliable.
|The Archdukes of Hell|