Nikolaus followed his brother Ludwig to Vienna in December 1795, expressing the wish to be known from then onwards as Johann, in memory of the brothers' late father.
Johann had trained in Bonn as a pharmacist and took a position as pharmacist's assistant in Vienna.
In March 1808 he bought an apothecary shop in Linz in Lower Austria, almost immediately falling into debt to such an extent that he was threatened with bankruptcy.
He first sold the iron gratings of the windows, but the small amount he made quickly ran out. He then had two pieces of good fortune.
First he discovered that the jars and pots on his shelves were made of pure solid English tin. Napoleon's ban on any trade in English goods raised their value enormously - Johann sold them for good money and replaced them with pots made of earthenware.
Then, in 1809, Napoleon invaded Austria and laid siege to Vienna. The French Emperor established his base camp in Linz and it was to there that he shipped his wounded soldiers. Johann van Beethoven was perfectly placed to supply all the French army's medical needs.
Thus Johann made his fortune - at the same time becoming enormously unpopular locally, since he had in effect collaborated with the enemy.
With his new-found wealth, Johann bought an estate at Gneixendorf, a village near Krems on the Danube west of Vienna, which Ludwig visited with his nephew Karl in the last full year of his life.
Ludwig's relationship with Johann was hardly less fraught than with his other brother, Carl. To begin with he simply could not come to terms with the apparently trivial decision of his brother to decide he should be addressed as Johann after his arrival in Vienna. In the famous Heiligenstadt Testament of 1802, addressed to his brothers, Ludwig could not bring himself to write the name 'Johann'. It is difficult to understand Ludwig's reasoning, other than as an awakening of a deep-seated resentment towards his father.
In 1812 Johann announced his intention of marrying his housekeeper in Linz, Therese Obermeyer . Ludwig was in the Bohemian spa resort of Teplitz, in the months following his own ill-fated love affair with the 'Eternally Beloved'. When he learned of Johann's intention, he left immediately for Linz to confront his brother and convince him of the unsuitability of his housekeeper as wife - a woman who would carry the name 'Beethoven'.
Johann, in no uncertain terms, told Ludwig to mind his own business; his choice of wife was his own. Ludwig, in characteristic fury, first tried to persuade the local Bishop to refuse to marry the pair, on the grounds - as he had discovered - that Therese already had a small daughter by another man. The Bishop refused to intervene. Beethoven then applied to the civil authorities to have Therese expelled from Linz on the grounds that she had no right to be living there. The authorities took no action.
Finally, it is said, the two brothers had a furious row and came to blows, after which Ludwig left Linz for Vienna. On 8 November Johann married Therese.
But this marriage - as with that of Carl and Johanna - was to be unhappy; the couple had no children. The American Beethoven scholar Maynard Solomon says that the three Beethoven brothers were simply ill-equipped for marriage.
Johann van Beethoven was not, by general recognition, a man of great intellect. When, after purchasing the estate in Gneixendorf, he signed a letter to Ludwig, 'From your brother Johann, landowner', Ludwig signed his reply, 'From your brother Ludwig, brain owner'.
Carl Czerny gives us a description of Johann as terse as that of Carl: 'Johann: large, dark, a handsome man and complete dandy.'
Gerhard von Breuning, son of Ludwig's best friend, Stephan von Breuning , gives a more voluble - and devastating - critique of Johann, which I quote (almost) in full.
'For some years after the death of the great "brain owner", his brother, the "landowner", played a strange, naive role. During Ludwig's life Johann's interest in his works was limited to possible gain from them; now he tried to present himself as an appreciative admirer. At concert performances of music by his deceased brother he would sit in the first row, all got up in a blue frock coat with white vest, and loudly shriek Bravos from his big mouth at the end of every piece, beating his bony white-gloved hands together importantly. These oversize gloves, with their flapping fingers, could often be seen elsewhere as well, in the elegant drives in the Prater ...
'All this pretentiousness and in general the overall appearance of Johann - who bore no physical resemblance to Ludwig: he had a long face, big nose, one eye squinting outwards, giving his face an expression of perpetual self-satisfaction - earned him the nickname of "Archduke Lorenz", from the familiar proverb about people who endeavour to put on a great show and conduct themselves ridiculously in the process. Johann died in Vienna in January 1848. He proved to be as preposterous after his brother's death as he had been contemptible during his brother's life.'