Otto von Kappf (c. 1856 - c. 1920), giornalista e poeta tedesco. Nato a Königsberg, si stabilì a Vienna dove per alcuni anni fu attivo come critico. Divenne amico di Busoni nel 1878. Secondo Dent «aveva un temperamento sentimentale e romantico in una figura modellata su quella di Re Luigi II di Baviera». Per otto anni fu sposato con la scrittrice femminista ebrea Franziska von Kapff-Essenther. Morì in in povertà.

«A concert in November brought him a letter from an unknown admirer who desired to make his acquaintance. Ferruccio was in no hurry. He had to prepare for another concert the following Saturday, and the admirer must wait till Sunday to present his compliments in person. On Sunday afternoon Ferruccio was busy, but he might call on Sunday mormug. Ferruccio at twelve might have been a business' man of forty, to judge from his method of making appointnents. The admirer called, and a friendship began which asted for the whole of Ferruccio's life. Otto von Kapff had ome from Königsberg, the most Prussian of Prussian cities; but his sympathies were with the south, and he eventually became in most of his habits a typical Viennese. His inborn Prussianism came out only in his rigid sense of honour; misfortune overtook him in later life, but he lived for years in poverty without ever having owed a farthing and without having ever asked help from any one. When he heard Ferruccio play at Graz he was not much over twenty. By occupation he was a journalist, by inclination a poet, and by temperament a romantic sentimentalist who modelled his appearance on King Ludwig II of Bavaria. His face was fat and puffy, with small eyes and large loose lips. His outward appearance was, however, somewhat variable; one day he would be photographed in a fur-trimmed coat and a profusion of jewellery, another day as a sort of Caliban with hair and beard that looked as if they had never encountered brush and comb in their whole existence. Ferruccio accepted his devotion as a matter of course. He was flattered at having a grown-up friend of his own and was quite prepared to meet him on equal terms. Kapff sent him poems; he set them to music -when they were suitable. If they were not, he told the poet so - politely, but as one artist to another. Kapff seems to have feared that his letters might appear too sentimental; Ferruccio, no doubt reading with an Italian eye for fine phrases, was delighted with them, but replied in language more business-like. Kapff offered romantic adoration; Ferruccio realized at twelve years old that a virtuoso can make good use of a press-agent and general factotum.» [DENT, pp. 27-28]