He was born in Frankfurt, the son of a well-known Jewish wine dealer. In 1938, after the Crystal Night pogrom, the Nassauers retreated from the Nazi menace and moved to London, abandoning the family business with its network of interests in some of the best vineyards in Germany. The father went first, leaving his wife and Rudi - aged only 14 - to deal with the Nazi bureaucracy as the family property was surrendered. In London, after the war, the business revived as Nassauer & Son, trading in German wines from a tiny office next to Charing Cross station.
Rudi went into the firm, and loyally took over when his father died. At the same time, he began to write. Two novels above all will last: The Hooligan (1960) and The Cuckoo (1962), both works of terrifying imaginative power which drew on his experience of the Nazi mind and his own tormented personal relationships. I suppose it's true that being a wine merchant interfered with his writing; without the business, there might have been more novels. But at a deeper level the two occupations fed into one another. He bought and sold with the bold and capricious style of a creative artist; he wrote with the combination of ruthlessness and mind-reading empathy that a true merchant requires.
Business meant going back to Germany. It often meant negotiating with the same dealers and growers who had been his family's clients in the old days - and who, like jackals, had gobbled up fragments of Nassauer property as the Nazi authorities tore it apart. Members of his family who had failed to escape in time had perished in the gas chambers. The ironies of all this sometimes entertained and sometimes revolted him, making him an even more complex character. He was a despot and a jester, funny and savage by turns.
Once I accompanied him on his annual wine-buying journey through the Rheingau vineyards. At the end of the trip, he had to select his main table-wine for the next season and we found ourselves in the cellars of one of the great wholesalers at Mainz. The partners stood about in rusty suits, among banks of open, unlabelled bottles. A reverent hush fell. The firm's chief taster, a thickset young man with a face like a mandrill, tiptoed from one bottle to another. The only sound was the crunching as he swilled the wine around his teeth and the coppery "bong" as he squirted it out into the spittoon. Then Rudi began his tasting.
The tension rose as the choice narrowed. The partners leant forward, pressing their fingertips together. I could feel in Rudi a gathering impulse of rage and impatience at all this solemnity. Then it was down to a choice between two bottles. And suddenly Rudi pulled a coin out of his pocket.
"Heads this one; tails that!" he said in English. He spun the coin. I looked around at the ring of German faces: frozen, thunderstruck. It was one of the funniest moments of my life. But nobody laughed - certainly not Rudi. It was a joke too deep for laughter. It was also a gesture of terrible, almost murderous aggression, a blasphemy aimed at a certain caste in a certain nation.
It was on that same journey that I learnt what trade really is. Growing up in the war and the 1950s, I had never sold anything but a Mozambique stamp to a schoolfriend, or bought anything more speculative than a pair of socks. Trade existed on the margin of my consciousness, something spivvish. But from Rudi I learnt that trade is inherent to being human. Any European hole may reveal Portuguese sardine cans, Flemish jug fragments, bits of Samian ware from Roman factories on the Rhine, gold wire from Bronze Age Ireland, even flint brought by Neolithic pedlars from mines in Norfolk. But trade is not just a matter for history theses. It is an emotional relationship, not unlike a sexual seduction.
Watching Rudi, in the house of some rich peasant on the hallowed soil of villages like Erbach or Eltville, I saw this courtship being developed as it has been practised since trade began. The other mind has to be delicately entered by the trader and then scouted, as softly as a cat moves round a mouse, to see if it contains any obstacle to agreement. This other mind is of course aware of the scouting, and can halt or reject it by a minute sign at any moment. But if no obstacle is found, no warning of rejection signalled, then this infinitely subtle exploration advances until it reaches a critical point at which "Yes" is implied because it has not been denied. The closing of the deal is then brought about by a look, a movement, a slight change in the tone of voice or some other almost subliminal scrap of body language. And it's on.
In each farm parlour I leant forward, craning to hear every word. And yet, however hard I tried, I still could not grasp the process. Rudi and the German winegrower would talk slowly and casually about apparently haphazard things: the snow last spring, the rain that summer, the moisture or dryness of the earth. Other farmers, even local politicians, might be mentioned in an aimless way. Sometimes the two men would let fall remarks about wine prices, but always referring to some other place neither very close nor very far away. And then suddenly they would be getting to their feet. Rudi would pull out a notebook and write down a few words and figures. The farmer would leave the room, murmuring a few words to his wife in the kitchen, and return with an open bottle of his own private Spatlese.
And I had missed it again. The bargain had been struck - but when and how? Afterwards, as we sipped the wine, there would be practical talk about bank accounts and deliveries. But I never picked up the critical moment, the words with which the buyer and the seller told one another that the deal was on or off (because occasionally nothing was written in the notebook and we left politely but without ceremony) or that the price was too high or too low.
And in the end I understood that they never did say those words. The communication between them was not telepathic, and not even exactly wordless. Instead, both individuals were using movements, pauses, words selected for mood indication rather than "meaning", as a single hypersensitive code. To know that code, and to be able to enter the state of super-alertness which it requires, is the ancient secret of merchants.
Diplomats, or at least good ones, have that secret, too. Some years ago, before communism collapsed, I was on the British delegation to one of the "Helsinki" conferences on European security and co-operation. Things got deadlocked; one delegation - I think it was the Romanians - was holding everything up over some trifle of wording. In the plenary meetings, we made angry speeches about the trifle, which got nowhere. But a professional diplomat, an elderly English ex-ambassador, took a Romanian aside and sat down with him on a sofa. I edged up and listened. They made a few jokes to each other about the way the conference was run, and exchanged a few cliches about the general state of East-West relations. Then the Englishman got up.
Noticing me, he said: "Well, that was easier than I expected". "What was easier?" But, just as in the Rheingau farm parlour, I had missed the crucial subtext under the spoken banalities: the spark of agreement.
Negotiating in subtext can be hard on the nerves. When that German trip was over, we went off to the casino and Rudi flung money away at the roulette tables. Once, he confessed, his patience had snapped and he had shouted at a farmer that he knew what he had been up to during the Third Reich. Paralysed with shock, the grower had sold him wine cheap. Rudi felt a bit ashamed of that episode. But not entirely.