The ill-fated mountaineer George Mallory's only book was "Boswell the Biographer"?
Adolf Heinrich von NeitschützBorn 1730
Referred to by Boswell only as "Neitschütz", he is almost certainly Adolf Heinrich von Neitschütz (1730-1772), sometime Stallmeister in Anhalt-Dessau.
Possibly the von Neitschütz who married (1765) Johanna Eleonore Hoffmeier (1746-1816), sometime mistress of Leopold III with whom she had an illegitimate child, Count Franz von Waldersee, in 1763.
Life with Boswell:
Boswell met Neitschütz on the first day of his visit to the Court of Dessau on September 24, 1764, and noted that he, Neitschütz, had been very kind to him.
On September 27, Neitschütz gave Boswell a tour of the Dessau palace, and afterwards the two "mounted a couple of the Prince's horses [...] and went and saw his Polish and Hungarian cattle."
On September 28, Boswell "rushed boldly along with the Herr Overstalmeester, as they called my friend Neitschütz" during a hunt.
When Boswell left Dessau on October 1, he noted intending to keep up a correspondence with Neitschütz and Berenhorst, but, as was the case with most of the friends he made during his tour of Germany, he apparently never did. The two met again at Leipzig just three days after Boswell left Dessau. Neitschütz was there to “sell some of the Prince's horses” at the Michaelmas fair. They dined together, with O'Grady, on October 5.