Engineering legend Ulrich Hackenberg retires from VW Group

Ulrich Hackenberg, one of the most influential and prolific car engineers of the modern era, retired from the VW Group last week. It was an unscheduled exit.

The extraordinary flowering in the number of different models built by the Group in recent years is a direct result of Hackenberg's work. It's why they could make the latest Audi TTS so different from, say, the Skoda Superb TDi and new plug-in VW Tiguan GTE. And more important, do it at a profit.

For it was Hackenberg who came up with the 'modular kit' approach to car making. Before that, manufacturers built 'platform-shared' machinery that was profitable but created cars too alike. Or they had to develop very separate underpinnings, which made many niche models unjustifiable.

Hackenberg's 'kits', or in German 'Baukasten', were absolutely rigid in defining certain dimensions of the cars – suspension mounts, the relationship between the engine and pedals, for instance. Also the slots for the air con and infotainment systems, and the electrical architecture. This means the powertrain and crash structures, and the assembly lines, can be made common. These are the really big investments where sharing pays off.

But it also means much of the rest of the car can be varied, so they're not all boringly similar.

Hackenberg was in charge of product strategy at Audi when he devised the first of his kits. This was the MLB, the longitudinal-engined kit that saw Audi build aluminium and steel saloons (A8 to A4) and Bentley make its big coupe, the Continental GT.

Once he'd nailed that, Hackenberg moved to VW and embarked on his transverse-engined kit, the MQB. It was the pinnacle of his life's work, co-ordinating four brands, and cars all the way from supermini-sized to seven-seat SUV. We haven't seen the half of them yet. They come as petrol, diesel, hybrid, plug-in hybrid and pure electric.

Five million MQB vehicles will be built each year by about 2018. That's a spectacular monument to one man's vision.

Hackenberg wanted to leave it at that. But two and a half years ago he was called in by Audi for one last job. People who knew him say he didn't really want it – he several retirement projects in mind, including building a spectacular house.

The Audi job was a homecoming of sorts. Hackenberg had worked there from 1985-98, and 2002-07. (In between he'd been at Bentley and VW.) But Audi wasn't in an altogether good place. It was making money, but the future pipeline was scant. Audi had dropped the innovation ball to BMW's i brand, and the style ball to Mercedes.

Hackenberg quickly brought in design chief Marc Lichte to sort out the style. You'll see a step-change from the pre-Hackenberg conservative A4 and Q7, to the more radical new A8 and A6. He also fast-tracked electrification projects such as the upcoming electric Q6 eTron and revived the R8 eTron.

So why did he go? Audi is saying nothing. All its official statements do is praise his contribution over the past 30 years.

I have never met an engineer who knew more detail about the cars developed under his watch than Hackenberg. That's part of what made him so great – not just the big picture but the smallest specifics. He was head of R&D at Volkswagen during much of the era when it was selling the cars now part of the emissions scandal.

Hackenberg will have come under intense suspicion that among the detail he knew about was the critical engine software code. Since the scandal broke he has been, according to many reports and some VW sources, under suspension. But the enquiry has not yet reported and no evidence against him has been made public.