Who is Aristotle Quance from Tai-Pan and what is their importance?

Quance is an artist that appears on and off throughout the book. He is half English and half Irish and is fifty-eight years old and has lived in Macao for more than thirty years. He is present at the ceremony of Hong Kong being given to the British and paints the scene. He is also present at the land sale and is chosen by Dirk to judge the contest for the best dressed woman at the ball.