Ivan Ivanovich Sollertinsky (3 December 1902 in Vitebsk – 11 February 1944 in Novosibirsk) (Cyrillic: Ива́н Ива́нович Соллерти́нский) was a Soviet polymath. He specialized in fields including linguistics, theatre, literature, history, and philology, but was most known for his work in the musical field as a critic and musicologist. He was a professor at the Leningrad Conservatory, as well as an artistic director of the Leningrad Philharmonic, and a prominent orator. In these capacities, he was an active promoter of Mahler's music in the Soviet Union. Sollertinsky was also interested in ballet and often wrote essays on the subject during the 1930s, along with teaching ballet history at the Leningrad Choreographic Institute. According to contemporaries – most famously Irakly Andronikov – he had a phenomenal memory, and supposedly spoke 26 languages and 100 dialects. However, Nicolai Malko claimed that Sollertinsky was able to speak 32 languages, some of which were also considered dialects.