Who is Yakub Beg from Flashman at the Charge and what is their importance?

Yakub Beg is the real life ancestor of Timerlaine the Great. He actively uses his role in the military to prevent a Russian take over of the lands east of the Caspian Sea. Flashy first meets Yakub while he is imprisoned by the Russians. When Flashy and Yakub escape the Russians, they travel to Beg's estate in the Kizil Kum.