Short answers, pulled from the story.
Polystylism is Alfred Schnittke's compositional method of juxtaposing and combining music from different styles, eras, and traditions within a single work. He described his goal as unifying serious music and light music. His first concert work to use the technique was the second violin sonata, Quasi una sonata, composed in 1967-1968.
Alfred Schnittke converted to Catholicism on the 18th of June 1983. He began seeking solace in the faith during the composition of his Piano Quintet, which he wrote in memory of his mother after her death in 1972. His beliefs in predestination and mysticism influenced his music.
Alfred Schnittke was banned from travelling outside the USSR after he abstained from a Composers' Union vote in 1980. His First Symphony had already been effectively banned by the Composers' Union, and his music was often viewed suspiciously by the Soviet bureaucracy.
Alfred Schnittke was born on the 24th of November 1934 in Engels, in the Volga German ASSR of the Russian SFSR. He died on the 3rd of August 1998, in Hamburg, Germany, at the age of 63, and was buried with state honors at Novodevichy Cemetery in Moscow.
Schnittke wrote his Ninth Symphony with great difficulty using his left hand due to his strokes, making the score nearly unreadable. After hearing the premiere on the 19th of June 1998 in Moscow, conducted by Gennady Rozhdestvensky, he indicated he wanted it withdrawn. After his death, Alexander Raskatov completed a decipherment; that version premiered in Dresden on the 16th of June 2007.
After leaving the Moscow Conservatory in 1972, Schnittke earned his living chiefly by composing film scores, producing nearly seventy scores over roughly thirty years. His film work also served as a laboratory for developing his polystylistic technique.