Sergei Diaghilev's most enduring influence on twentieth century art was the Ballets Russes, a modern ballet company he created, starring the greatest male ballet dancer of the twentieth century and Diaghilev's lover, Vaslav Nijinsky.
In the early twentieth century, the Russian Sergei Diaghilev was the "bad boy" of the Russian art world. It's safe to say he was the most important figure in twentieth century art who was not himself an artist.
The United States intervenes militarily in Cuba and elsewhere in Latin America. A great earthquake strikes San Francisco, triggering racial discrimination and an economic downturn. The Brownsville Affair. And Roosevelt takes "In God We Trust" off the $20 coin.