Very little is known about this one ...
Apparent son of Bane, on some sort of mission to please a father who rejected him. Or so says Rhosius. He was defeated at one point by the Harpers, with significant outside help, but the story is not well known outside of those who survived it.
The Zhentarim appear to serve him. An army of Gith led by someone named named Zalthair seems to be doing his bidding as well.
Abraham appears to require “heirs” for sacrifice. But for what purpose exactly?