Who is Vice Minister Zai from Dragon Bones: A Novel and what is their importance?

Vice Minister Zai serves as a figure to Hulan. He took her under his wing after the denunciation of her father, and his death. Zai is both an employer and caretaker of Hulan. Hulan eventually learns, however, that his primary focus will always be the protection of China, even at the risk of Hulan's and life.