This man is in a class all by himself.
He seems to be a connection to a forgotten world, a world where money wasn't the most important thing to everyone. Don't get us wrong, "Dr. Gu is worth hundreds of millions" (2.16.13). But he isn't consumed with acquiring more money, flaunting his money, or even talking about it.
He and Goh Wye Mun met years ago when Dr. Gu refused to sell his house to Wye Mun, instead convincing him to change his entire business plan. This change essentially led Wye Mun to become the tycoon developer he is today. For that, the two have stayed friendly.
When the Gohs see Dr. Gu to find out more about Tyersall Park and Sir James Young, Dr. Gu is brought back to a world when money moved invisibly behind walls and life had different meaning. Dr. Gu was saved by James Young during World War Two and feels guilt over revealing so much about the Young's money, rather than focusing on the charity and goodness of the man.
Gu does, however, offer some warnings: "Prosperity is nothing but an illusion" and "every treasure comes with a price" (2.16.25 and 2.16.75). The Shaws will come to illustrate the first adage, and Rachel will come to realize the second.