"Pit Fiend Ex-Lord of Avernus"
A powerful Pit Fiend general of the First Layer of Hell, for a brief time ruler of the first layer, before being replaced by the fallen angel Zariel by Asmodeus. This change of power, according to Lord Volmer, angered Bel, who is now out to spite Zariel.
In this case, spiting Zariel is to foil her plan to be rid of Tiamat, working against the fallen angel’s servants in the Prime Material Plane to foil the working of the Cult of the Dragon.
For the brief time that Zariel did not hold the throne of Avernus, Tiamat tore into the angel, like a play thing. Bel hopes to one day bring that pain to his rival again.