When Russians look at Iran, they see a country that has been their neighbor and rival forever. As the Russian empire advanced, it wrestled the North and South Caucasus from the Shah. Peter the Great annexed, briefly, Iran’s entire Caspian Sea coastline and put his forces just north of Tehran.
In the early 20th century, Russia and the U.K. divided Iran into zones of influence. The Russians got the north and proceeded to occupy Iran twice, during each of the world wars. When Franklin Delano Rooseveltand Winston Churchill met with Josef Stalin in Tehran in 1943, they were protected by the Red Army.