Historians don't doubt that Peter Tchaikovsky was gay, but an upcoming biopic filmed in his native country will. Yuri Arabov told a Russian newspaper that his adaptation of the 19th century composer's life won't focus on his sexuality because “it is far from a fact that Tchaikovsky was a homosexual," The New York Times reported.

Arabov also said that films that "advertise" homosexuality are "outside the sphere of art," and that only "philistines" think the composer was gay. In light of Russia's recent anti-gay legislation, this could be seen as another effort to erase the country's gay history. Well, sorry Russia, but Tchaikovsky — along with dozens of other Russian cultural icons — were gay, as many scholars would readily attest. 

Pyotr Tchaikovsky (composer)

Tchaikovsky composed two of the most quintessentially Russian ballets — Swan Lake and The Nutcracker. And as Christopher Harrity described in The Advocate, Tchaikovsky's sexuality was well known, and also well documented in his own letters. Harrity writes (emphasis added):

The history of Tchaikovsky's homosexuality was suppressed in Russia by the Soviets, and it has only recently become widely known in post-Soviet Russia. Tchaikovsky's letters and diaries, as well as the letters of his brother Modest, who was also gay, make clear his orientation. [...] Many of Tchaikovsky's most intimate relationships were homosexual: Tchaikovsky's servant Aleksey Sofronov and his nephew, Vladimir “Bob” Davydov. Gay author E.M. Forster referenced Tchaikovsky and Davydov in his love story Maurice, written in 1913-14 and published in 1971: “...Tchaikovsky had fallen in love with his own nephew, and dedicated his masterpiece [Symphonie pathetique] to him.”

And as The Independent reported in 2009, a biography by Roland John Wiley found definitive evidence of sexuality:

A new biography by Roland John Wiley was published this autumn and ecstatically reviewed in these pages by Michael Church; it claims that some of those mysteries are no more than myths. For instance, Wiley points out that Tchaikovsky was openly gay all his life, to the point that he feminised the names of the young men he consorted with, and indeed his own – signing a letter to his brother (who was also gay) "Petrolina".

Nikolai Gogol (author)

The 19th century novelist, best known for Dead Souls and his short stories, was also homosexual. The Sexual Labyrinth of Nikolai Gogol, by fellow gay Russian Simon Karlinsky, argued that evidence of Gogol's homosexuality could be found in his works. In her review of the book for The New York Review of Books, Helen Muchnic laid out Karlinsky's argument this way:

His thesis, in brief outline, is that Gogol, unable to be himself in a world where homosexuality was proscribed, concealed his inclinations, attempted to suppress his emotions, projected his secretiveness unconsciously in the deceptions, mystifications, and symbols of his stories and plays, and ultimately broke down under the strain, ruining his art and destroying himself. 

There are also references to Gogol's sexuality here and here, among other places. 

Sophia Parnok (poet) 

Parnok, who died in 1933, was known as the Russian Sappho and wrote about her sexuality in her poems. Here's an excerpt from her 1924 poem "Dreams": 

Only in dreams, with a broken off moan,
so as not to die in her sleep,
on such a mellifluous wave,
above this sky-blue drowning,
her whole chest heaving freely
with breath, my soul is bobbing.

Parnok published several collections of poems until censorship under the Soviet government deemed her works "unlawful" in 1928

Sergei Nabokov (brother of Vladimir Nabokov)

Vladimir Nabokov, best known for his 1955 novel Lolita, was a known homophobe. Yes as Lev Grossman explained in this 2000 piece for Salon, his brother was a known homosexual. Grossman wrote:

Sergei’s homosexuality would cast a long shadow over his strange and heroic life, and it would also, ultimately, be the cause of his horrifying and untimely death. It cast a shadow over Vladimir’s life as well: He loved his brother, but whatever else he may have been — a brilliant writer, a loving father — Vladimir was a confirmed homophobe, and his gay brother was a constant source of shame, confusion and regret to him.

Sergei died in a Nazi labor camp, while Vladimar went on to write several novels. Meanwhile, gay characters appear throughout Vladimir's work, possibly in recognition of his brother.