In Russian history, it’s Nicholas I, Gorbachev, and Yeltsin. Nicholas I, under the guise of conservatism, caused degradation, the apotheosis of which was the Crimean War, during which it became apparent that the country lacked proper roads, and after the war it was revealed that there were no reserves of weapons. Due to the rule of Gorbachev and Yeltsin, the demographic termin “Russian cross” emerged.
Edit: There was a question about Putin in the replies: I do not believe that Putin has caused more harm to the country than external influences and certainly less than the three leaders I mentioned.