Riaan Stassen is surely one of SA’s most successful banking entrepreneurs. Last week he announced his retirement as chairman of Capitec, leaving the bank he helped found only 18 years ago with one of the highest market valuations (on a price-to-book basis) in the world.

While Capitec is still a small bank on most measures — its R100bn balance sheet is one-thirteenth the size of Standard Bank’s, the largest in the market — it has caused an outsized level of disruption. That is clear in Capitec’s market capitalisation of R156bn, which places it third behind Standard Bank and FirstRand. With 11.4-million customers, it is among the biggest, with only Standard Bank having more, and only just.

Stassen’s influence is clear in the DNA of the bank. He is disarmingly approachable and casual. I doubt he has ever worn a tie in his career. But that was true of Leon Kirkinis too, the very likeable CEO of African Bank, which collapsed into curatorship four years ago.

The difference is that Stassen has shown an almost steely focus on evolving Capitec and ensuring it can be managed with razor-sharp analytics. He is famous for being able to tell you the exact performance of the loan book on any day. He ensured Capitec started out with simple but powerful and scalable systems that would allow him to track performance in near real-time, from the number of transactions through ATMs to the time taken to serve customers in branches. He saw that getting systems and processes right leads incrementally to competitive advantage.

That incrementalism is clear in the evolution of Capitec’s balance sheet. Its starting point was low brow — a bank funded largely by shareholder funds making short-term loans, much like any other microlender. But, little by little, it evolved both the funding side and the asset side of the business. That evolution is still in progress, with deposits creeping up as a proportion of funding (therefore lowering overall funding costs) and transactional revenue creeping up as a proportion of revenue.

The loan books have also been extending outward, going into longer-dated, more traditional, forms of lending. With the acquisition of Mercantile currently being considered by regulators set to move it into commercial banking, Capitec is starting to look ever more like a “normal” bank.

But the bank’s DNA is unlike any other major bank. It operates from a rather drab office park outside Stellenbosch, though a new purpose-built campus is under construction next door. The small office Stassen occupied as CEO until 2014 had no art on the walls and hasn’t had any added since Gerrie Fourie, the current CEO, took it over. There are none of the usual trappings found in banking head offices in Johannesburg — no sweeping foyers or contemporary art collections. Stassen was always clear that shareholders’ money should not be wasted on corporate fancy.

Capitec has had to weather several crises — founded in the midst of the small banks’ crisis at the start of the century, listing in 2002 just six months before Saambou’s collapse that led to the end of BoE, and trading through the collapse of its largest rival African Bank. Each of those led to market fears about Capitec. That left Stassen with an obsession about risk and determination to operate as efficiently as possible. Perhaps it is this that will continue to be Capitec’s core differentiator and maintain its competitiveness, even as it otherwise grows into a more traditional bank.

Capitec’s growth rates and market ratings have forced the other banks to take note, and not always in a good way. Its big four rivals were forced to respond with a more aggressive move in the unsecured lending market, the area Capitec dominated. In the process, overall volumes into that market skyrocketed as all the banks attempted to emulate Capitec, triggering a competitive race that has contributed to a widespread over-indebtedness problem, with more than 9-million South Africans now classified as overindebted.

Ironically, the one area of Capitec that is actually shrinking is its earnings from unsecured lending. Growth is now in transactional banking, the more traditional product of its larger rivals. In that area, Capitec is showing that simplicity and customer service can drive competitive differentiation, with hundreds of thousands of new clients signing up every month.

It was perhaps his early career in retail with Distell that positioned Stassen to think differently to the usual banking approach. He was encouraged to join Boland Bank by Michiel le Roux who had been his boss at Distell. When Christo Wiese (of more recent Steinhoff notoriety) merged Boland with NBS, Le Roux and Stassen took a core team from Boland to set up Capitec. Their initial funding came from PSG’s Jannie Mouton and PSG remains the largest shareholder in Capitec, an investment that has paid off big time.

The bank has made Stassen a wealthy man, with his shares pushing him into the billionaire league. That has not only afforded him the usual Stellenbosch trappings of a wine farm (Happy Valley) but also a keen enthusiasm for Formula 1 and team Ferrari, several of which he has owned. One of his fellow board members tells me that it is Ferrari’s obsession with detail and incremental improvement that attracts Stassen to the brand.

One hopes it is has been baked into the DNA of Capitec for the long term.

• Theobald is chairman of Intellidex.