Iran became Russias most loyal ally after the Islamic revolution in 1979. This relationship has lasted over two decades, and is still cherished by the Islamists among Shiite clergy and security services. When Soviet troops invaded Afghanistan later the same year, there was only one spontaneous demonstration in Tehran, after which Iran has tamely followed Russias actions against neighbouring Muslim people.
The Iranian revolution took the KGB by surprise, but it was a pleasant surprise, and the Soviet Union choose to side with the Islamist revolutionaries already by November 1978.