Short answers, pulled from the story.
Serbian refugees found sanctuary within Russian borders after fleeing their homeland following the Ottoman invasion in the 14th century. Lazar the Serb and Pachomius the Serb became notable figures in medieval Russian history during this period of displacement.
Konstantin Rodofinikin proposed that Serbia become a protectorate of the Russian Empire with Russian garrisons stationed throughout the country in 1807. Karađorđe refused the proposition because he believed it would turn Serbia into merely another Russian province rather than an independent ally.
Department IV of the Russian All-Military Union operated from Belgrade headquarters with constant liaison to Yugoslavia's Ministry of the Army and Navy. The organization counted 25,000 members within the Kingdom of Yugoslavia by 1934.
Member countries adopted a resolution expelling Yugoslavia from the Information Bureau on the 28th of June 1948 at the second conference of the Cominform. Tito did not attend this meeting while Stalin took the matter personally and attempted unsuccessfully to assassinate Tito on several occasions following this diplomatic rupture.
More than two-thirds of Russian exports consisted of natural gas transported through the TurkStream pipeline providing for some 90% of Serbian annual natural gas consumption. Trade between two countries reached almost $3 billion in 2023 with Russian merchandise exports totaling about $1.7 billion and Serbian exports standing at roughly $1.2 billion.