Nicholas Van Rijn

This image shows the covers of Volumes I-III of Baen Books' seven volume The Technic Civilization Saga:

Vol I, The Van Rijn Method, collects the first eleven installments of Poul Anderson's History of Technic Civilization;

Vol II, David Falkayn: Star Trader, collects the next seven;

Vol III, Rise Of The Terran Empire, collects six.

I think that a better distribution of installments between these three volumes would have been nine, nine and six. Thus, Vol I, having introduced Nicholas Van Rijn in "Margin of Profit," would culminate with the first van Rijn novel, The Man Who Counts. After that, van Rijn becomes a major sub-series character dominating Vol II and appearing in a total of ten of the forty three installments of the Technic History.

In my preferred version of Vol II, van Rijn:

is the central character of "Esau," "Hiding Place" and "Territory";
cameos in "The Trouble Twisters," where he founds the trader team led by David Falkayn;
is again the central character of "The Master Key," although in this story his role is to comment on the actions of several other characters;
is mentioned in "A Little Knowledge";
co-stars with the trader team members in Satan's World and "Lodestar" - as finally in Mirkheim, the opening installment of Vol III.

I have skipped over only "Day of Burning," a trader team story, and am currently rereading this installment to check whether Falkayn or his companions mention their employer, van Rijn, by name. This is what happens if you take Poul Anderson scholarship seriously.

Addendum: Not the central character of "Esau" but in conversation with Emil Dalmady.