In the Syrian civil war, Iranian and Russian forces have fought side by side to keep Bashar al-Assad in power. But cooperation between Moscow and Tehran goes back much further, explains Oved Lobel:
[T]he Islamist regime has maintained a deep warmth for Russia, especially after 1988. The Soviet leader Mikhail Gorbachev was the only foreign leader ever to receive a personal letter from Ayatollah Ruhollah Khomeini (in 1989) urging him to consider Islam an alternative given the imminent collapse of Communism. . . . While the current relationship is a strategic alliance, the Soviet-Khomeini relationship was more akin to the Russo-Turkish alliance of today, in which their highest mutual priority—the destruction of U.S. influence—allowed them to compartmentalize irreconcilable ideological and geopolitical differences.
The most extreme example of this is Afghanistan, where Khomeini and Moscow came to an arrangement whereby Tehran could replicate its Islamic theocracy in Hazarajat, the area predominantly populated by the Hazara Shiite minority, while the Soviets shored up their Communist state in the rest of Afghanistan. . . . Following the sudden rise of the Taliban, Russia and Iran allied against them and backed the Northern Alliance. . . . But, following the U.S.-led invasion in 2001, the two countries collaborated in supporting the Taliban.
Since Vladimir Putin took the helm at the Kremlin, the relationship between the two has only grown stronger:
The clearest demonstration of the Russo-Iranian alliance was their joint intervention in Syria to preserve Bashar al-Assad’s regime, but their anti-U.S. alliance spans the globe. For instance, when the Palestine Liberation Organization (PLO) sought Iranian support during the second intifada, it went to Moscow to connect with the Islamic Revolutionary Guard Corp, resulting in the 2002 Karine A affair, when the Palestinian Authority tried to smuggle 50 tons of Iranian-supplied weapons into Gaza in flagrant violation of the Oslo Accords.
Read more on Middle East Quarterly: https://www.meforum.org/62821/whither-iran-tehrans-russian-connection