The Russian – Iranian relations affected some important historical events, such as the Iranian revaluation in 1979, and the disintegration of the Soviet Union. After the Iranian revolution, the Soviet tried to establish good relations with Iran but some regional events prevented that. Later, after the disintegration of the Soviet Union, Iran has found it necessary to establish good relation with Russia, in order to obtain international support in the light of hostility relation between it and the USA. On the other hand Russia found that Iran's influence in Central Asia and the Caucasus, which stimulates to cooperate with it to prevent NATO expansion there.
A Sat, study studied this question.