Possibly one of the most colorful characters in the novel, Oliver is a second cousin of Nick's, on the T'sien side. He encounters Rachel at Shang Su Yi's house and quickly takes a liking to her.
Oliver essentially functions as a cut-through-the-BS look at Shang Su Yi's family. Rather than the star struck, 'OMG these people are so rich and fancy' that we get from many outsiders, Oliver offers us dirt on the family members, helping us remember that these people are, at the core of it, just people. When asked why he doesn't refer to Dickie and Nancy as uncle and auntie, he says, "I personally feel that the honorific should be earned. Dickie and Nancy have never given a […] about me, so why should I bother?" (2.2.121).
He's snarky and flashy, but never cruel to Rachel. Though he is enlisted to help move Kitty Pong off Alistair, when we see how easily she takes the bait, we can't help but figure that Oliver knew he was doing the right thing for Alistair.