Who is Yeh-lu Ch'u-ts'ai from Time's Eye and what is their importance?

An astrologer and adviser to Genghis Khan, Yeh-lu is patient and intelligent. He is a tall man who is of high enough station to merit servants. Yeh-lu is intelligent and uses all of his influence to gain information valuable to Khan, in an attempt to further his own status. Yeh-lu is a civilized man and is chief administrator of the empire. He was born in one of the neighboring nations and had originally been brought into the Mongolian camp as a prisoner, but his intelligence had enabled him to rise to the top in this new world of illiterates in a short time. Yeh-lu used books and medicines confiscated from raids into China as a model for their new state, and bragged that Chinese medicine and methods he had obtained were responsible for saving many lives during an epidemic in Mongolia.