Roussel led a group of (exiled?) raffish Normans into Byzantium. He was employed by Emperor Romanus Diogenes as a Lieutenant.
Anna Comnena in her book “The Alexiad” describes Roussel (or Ursel as she refers to him) as thus:
“Now this man was a Frank by birth who had been enrolled in the Roman Army, reached a high pitch of prosperity, and after gathering a band, or rather quite a considerable army, of men from his own country, and also of other races, he immediately became a formidable tyrant. For when the hegemony of the Romans had received several checks, and the luck of the Turks was in the ascendancy, and the Romans had been driven back like dust shaken from their feet, at that moment this man too attacked the Empire. Apart from his tyrannical nature, what more especially incited him to openly establishing his tyranny just then was the depressed state of the imperial affairs, and he laid waste nearly all the Eastern provinces. “
His military record was not unblemished – at Mantizekt (1071) when he saw that the Greek’s position hopeless, he refused to send own men into battle. He rebelled against Isaac Comnenus and began his own conquest of Galatia. Isaac was defeated by the Seljuk Turks.
Roussel charmed his way back into Imperial favour. Roussel was sent by Emperor Michael VII Dukas to lead mixed force of Normans and Frankish cavalry against the Turks in Anatolia. Once deep into enemy territory, he again betrayed his trust and with his 3000 loyal followers, Roussel set up a self-declared independent Norman state along southern Italian lines. He managed to capture Caesar John Dukas, uncle of the reigning Emperor Michael and proclaimed John Dukas Emperor (1073).
Emperor Michael allied himself to the Seljuk Turks and persuaded them to eliminate Roussel’s state in return for the territory (1074). Roussel himself managed to escape and General Alexius Comnenus (later Byzantime Emperor Alexius I Comnenus) was sent to hunt him down. At Amasea – Roussel set up himself as Governor and so endeared himself to local population that they only agreed to his removal on being told, untruthfully by Alexius, that they would be blinded.
A period of imprisonment at Constantinople followed. When army of Nicephorus Botaneiates marched on capital (1077), Roussel was released by Emperor Michael who gave him one last chance. Invested with new regiment and inflicting a crushing defeat on rebels – Roussel turned traitor for third time and declared for usurper.
On the journey from Amasea to Constantinople, Alexius Comnenus had fallen victim to his fascination. When starving in prison, Alexius had secretly brought Roussel food. During his confinement, Roussel most probably often spoke to Alexius of Robert Guiscard in whose army he had formerly served.
Roussel was intelligent, cunning, and not without military skill.
His fate remains unknown – it is presumed that having turned traitor yet again, he was imprisoned, tortured and executed.