The Beggar Lord never wanted the job; a friend of Charon's from the days of the Stygian Republic, he was given the job because somebody had to do it. Since that time, he's been the roundoff function for the rest of the Deathlords, collecting those defectives that don't know how they died, don't have the mental composure for the Penitent Legion or where the argument between other deathlords over the soul is just too ridiculous to go on.
The Beggar Lord is, to put it mildly, the unliving incarnation of bitterness. He's about as mad as the Skeletal Lord, but it mostly manifests as the neurosis of a petty man rather than the fullblown psychosis of his soi-disant colleague. He is paranoid, he is depressed, and he's so incapable of sensation that he engages in private masochistic rituals in the hopes of once again feeling something. He really just wants it to end, but he can't summon up the courage to do so.
The Beggar Lord primarily exists to continue existing. As a side effect of this, he is one of the more savvy politicians in Stygia. Since Charon's disappearance, he has primarily served as the deciding vote on the Deathlords' council - the Ladies of Fate generally don't vote and the other Deathlords are happy that they don't. As a result, he is usually a swing vote, and a swing vote openly for sale. He collects souls from the other Deathlords, who tend to give him their dross - two here, three there, maybe a half dozen on a good day. It all adds up.
The Beggar Lord is sitting on one of the biggest repositories of souls in the Underworld, albeit lousy ones. None of the Legions wants to give up good material to the Seat of Golden Tears, so he mostly gets what nobody else wanted anyway. That's okay though, because the forges really don't care what you were before you enter, and it doesn't matter after you exit.