Clavell based his characters (loosely) on people who actually lived.
The Noble House was based on Jardine Matheson Holdings Limited. This is a Scottish company that was founded in China in 1832. (Here's the history, according to Wikipedia.)
Dirk Struan is loosely based on William Jardine. (Jardine was a physician. Dirk was not.)
Aristotle Quance may be based on George Chinnery. Artcyclopedia has links to some of his incredibly beautiful works. There's a self-portrait at the Metropolitan Museum of Art.
Robb Struan may be based on William Jardine's partner, James Matheson. Matheson was a member of Parliament, and a Baronet of the United Kingdom.
Jin-qua is based on How-qua , aka Wu Bingjian. Chinnery drew several portaits of How-qua. (Another portrait on Artnet, and another on rootsweb.)
Cooper-Tillman (company) is based on Russell & Co. (Samuel Russel and Abiel Abbot Low - scroll down here to see a portrait of Low.)
Shevaun Tillman is based on Harriet Low. She wrote a book about living in China in this time period. That may be her portrait by Chinnery, on the cover of the book. (OK, not that portrait...)
The Brock family is based on the Dent & Co. Dent & Company officially folded in 1867. There was a run on a bank in England, that drove them to the brink. Jardine managed to avert disaster by learning about the crash earlier. (Does this sound familiar?) In the sequel to Tai-Pan, Clavell says that Brock's company was replaced by another, founded by illegitimate descendent. You can see a painting of one of Dent's clipper ships here.
Gordon Chen is loosely based on Robert Ho-tung. Ho-tung wasn't actually born till 1862, so there's only a passing acquaintance with reality here. Ho-tung was Eurasian, but not descended from the Jardines. Ho-tung did become the compradore for the Jardines. (Scroll down here to see his portrait at Hong Kong University, and here to see a 1955 photograph, from Life.) Ho-tung was a noted philanthropist.