Abu ibn Walid was an Earth Empire nobleman, and Duke of Callisto.
He was one of those in line for the throne of the Empire. After the Seventh Doctor killed the Divine Empress at her request, he was made Emperor.
Once his alliance with the Brotherhood was revealed, Leabie Forrester started a revolution to overthrow him. He was deposed and Leabie became the new Empress. (PROSE: So Vile a Sin)