Priest and professor of church music history at the Moscow Conservatory (b. 1818; d. 2/14 January 1889), born Dmitry Vasilyevich Razumovsky (Дмитрий Васильевич Разумовский).
Tchaikovsky greatly valued Razumovsky's advice concerning traditional Russian choral singing, and sought his advice when composing his liturgical works.
Correspondence with Tchaikovsky
2 letters from Tchaikovsky to Dmitry Razumovsky have survived, dating from 1875 and 1877, both of which have been translated into English on this website:
2 letters from Razumovsky to the composer, dating from 1881, are preserved in the Klin House-Museum Archive.