The Union of Soviet Socialist Republics (U.S.S.R.), also known as the Soviet Union, was a pre-war, Communist state in Eastern Europe and Asia, consisting of 16 Soviet republics. In the Fallout universe, the USSR did not dissolve in 1991, and continued to exist well into the 21st century.
The Soviet Union had a consular service and a foreign service, and had strong consular relations with the United States. There was a Soviet consulate in Los Angeles (the one Natalia's grandfather worked at), suggesting that Soviet-American relations were good enough in 2077 that American and Soviet citizens were able to visit each other's countries. However, in propaganda, the Soviet Union was still being portrayed as a red communist enemy, allied with the larger Chinese threat.
During the Resource Wars, the Soviet Union was in no direct conflict with the United States, though they were tested in Defense Intelligence Agency simulations processed by the P.A.M. machine, although it is unknown what role they played in the Great War. The Russian Soviet Republic also had some sort of human mutation experiment program for creating super warriors.
The Soviet Union is mentioned in the biography of Natalia, one of the pre-made characters in Fallout, whose grandfather was a Soviet diplomat at the USSR's Los Angeles consulate.
The Molotov cocktail is named after the Soviet prime-minister Vyacheslav Molotov.
In Fallout 3, the Museum of Technology states that the Soviet Union, along with China, constantly refuted the American claim that they put the first man into space in 1961.
In Wasteland, the game which influenced the Fallout series, the Russian-led Soviet Union played a pivotal role.
↑ 1.01.1Manager's Terminal, Reply from City Treasurer: "Listen here you pinko Commie-eyed puke, I got your lily-livered defeatest e-mails. I ignored them because they made me THROW UP IN MY MOUTH! Do you understand we're fighting a war here?! Against the REDS? And the only thing standing between you and hot atomic Armageddon is ME and my base full of GIANT NUCLEAR MISSILES? Answer me this, Specialist Buttinski: if the American people are overrun by Kremlin Joe and his Chicom cronies, what good will clean drinking water be? Commander Devlin"
↑Fallout 3 Official Game Guide Game of the Year Edition p.85: "Michael Masters Michael Masters was an esteemed electronic and biological engineer before the bombs dropped. He doesn't remember much of the first years after D.C. was destroyed, but he does remember his human life and resents his Ghoulish nature (though he does appreciate the gift of longevity). He was extremely intelligent and jovial in his old life, but living as a Ghoul has made him very pessimistic and angry at the world. He sees his Ghoulness as a karmic curse, because he was attempting to keep America at the forefront of human mutation experiments, breeding super-warriors after being inspired by the work of the German, Russian, and Chinese doctors." (Fallout 3 Official Game Guide Game of the Year Edition Wasteland Census)