Who is Culum Straun from Tai-Pan and what is their importance?

Culum is the son of Dirk. He had been living in England and attending school when he and their family contracted the plague. Culum survived; many other family members didn't. He travels to Hong Kong to tell his father. Dirk makes him a partner and has him stay to help try to save the bankrupt Noble House. After Dirk obtains the money to save the company, Culum also stays to help out and learn the business.