Paul Nikolaus Cossmann was a German writer, editor, and publicist born Paul Nikolaus Cossmann.
He was the son of the cellist Bernhard Cossmann (1822–1910) and his wife Mathilde (née Hilb). The elder Cossmann had from 1866 to 1870 taught at the Moscow Conservatory (where Tchaikovsky was his colleague) before he decided to return to Germany with his family. They had settled first in Baden-Baden, but, in 1878, they moved to Frankfurt am Main where Cossmann became one of the co-founders of the Hoch Conservatory.
In 1889, while in Frankfurt, the second stop on his itinerary through Germany, Tchaikovsky met the elder Cossmann at rehearsals for his concert, and the composer was invited to dine with his former colleague later that evening. The two men had evidently not met since Cossmann's departure from Russia in 1870. An entry in Tchaikovsky's diary for 2/14 February 1889 reads: "Dinner at [Bernhard] Cossmann's. He has aged awfully. Pleasing wife and daughters. […] Home. Unpleasant realization of failure. At Cossmann's. Supper. Their warmth and kindness". Despite some problems at that day's rehearsal and his misgivings about the conservative Frankfurt audience, Tchaikovsky's concert the following day, on 3/15 February 1889, at which he conducted his Suite No. 3, had turned out to be a huge success. He left Frankfurt already the next morning to travel on to Dresden (where he gave another concert before Berlin), but the Cossmanns had seen him off at the railway station, and it is likely that they told him that their son, Paul, was studying in Berlin, and asked him to get in touch with the young man, which he duly did while in the German capital on 15/27 February that year. Tchaikovsky also corresponded with Paul's older sister, Lulu Cossmann, who became a schoolteacher.