Short answers, pulled from the story.
Alexander Glazunov was a Russian composer, conductor, and music teacher of the late Romantic period, born in Saint Petersburg in 1865. He is significant for reconciling nationalist and cosmopolitan traditions in Russian music, and for directing the Saint Petersburg Conservatory from 1905 to 1930 through revolutionary upheaval. His students included Dmitri Shostakovich.
Glazunov was brought to the attention of Nikolai Rimsky-Korsakov by Mily Balakirev when Glazunov was around 14 or 15 years old. Rimsky-Korsakov took him as a private student, and by spring 1881 considered him a junior colleague rather than a pupil. Rimsky-Korsakov premiered Glazunov's First Symphony in 1882, when Glazunov was only 16.
Belyayev was a wealthy timber merchant who became Glazunov's most important patron after hearing his music in 1882. He took Glazunov on a European tour in 1884, founded a publishing house in Leipzig in 1885 that initially published Glazunov's work at personal expense, and launched the Russian Symphony Concerts series, inaugurated in the 1886-1887 season.
Glazunov conducted the premiere of Rachmaninoff's Symphony No. 1 in 1897, and it was a failure that triggered a three-year depression in Rachmaninoff. Rachmaninoff's wife later claimed Glazunov appeared drunk during the performance, an account given some credibility by Shostakovich's description of Glazunov keeping a hidden bottle of alcohol at the Conservatory.
Stravinsky began as a deep admirer: at 15 he transcribed one of Glazunov's string quartets for piano and modeled his own Symphony in E on Glazunov's symphonies. The relationship soured over time; Stravinsky later called Glazunov one of the most disagreeable men he had met, while Glazunov publicly dismissed Stravinsky's Feu d'artifice as "no talent, just dissonance" and declared in 1912 that Petrushka was "not music."
Glazunov left in 1928 under the pretext of attending Schubert centenary celebrations in Vienna, and never returned. He settled in Paris by 1929, claiming his continued absence was due to ill health. This fiction allowed him to remain respected in the Soviet Union, unlike Stravinsky and Rachmaninoff. He formally resigned from the Conservatory in 1930.