Shiko You

Shiko You is a doctor who took care of Shuurei when she was young and sickly. While he lives outside the capital, his medical expertise is renowned and his old friend Advisor Sho calls him to the capital to consult about the plague in Sa province. Dr. You teaches the imperial doctors how to surgically remove the worms that cause the disease.

[Spoiler] Later, he is revealed as another of the Eight Sages (the Sage of Ko, Yellow Immortal). Like Advisor Sho, he looks much younger in his sage form. [/Spoiler]

(Source: Wikipedia)