Mikhail Botvinnik was a positional player who favored closed positions with slow burning strategy. He offered the opinion himself that he was perhaps not the best tactician. Just the same his games showed he could play that way too when he needed to.
He dominated Soviet and World chess for many years. He was instrumental in the development of the World Championship providing much input into how it should be contested. His opinion on how Soviet chess should be structured in order to bring fresh talent through also held a lot of weight.
As a result his fingerprints were all over the successful chess organization in the USSR that produced the players that would dominate World chess from the 30s right through to the 90s.
Several of the former Soviet republics like Russia, Ukraine, Armenia, Georgia, Azerbaijan and others are still among the top chess nations today. Mikhail Botvinnik certainly played his part in that.