Complex sentence: Though possessing the name of a leading Byzantine aristocratic family, very little is known of Alexios' ancestry, and the name Doukas was also used by many families of humble origins.
Split into simpler sentences: Though possessing the name of a leading Byzantine aristocratic family, very little is known of Alexios' ancestry. The noble Doukas clan were not the only Doukai, as the surname was also employed by many families of humble origins.