Mikhail Gorbachev, "a man we can do business with."  But the advice he received was a cause of his downfall.  The West advocated an immediate change to a free economy, despite the then current deficits in basic essentials like food; it led to mass speculation, and the start of the oligarchs.  Secondly, the West suggested our very adversarial form of democracy, majoritarianism, even though in Russian translation the word is (or rather was) 'bolshevism' (большевизм).  Thirdly, the right of self-determination  --  if Ireland can opt out of the UK, Northern Ireland can opt out of Ireland, apparently; so, for example, if Georgia opts out of the USSR, Abkhazia and South Ossetia can opt out of Georgia; in a Union of over 50 ethnicities, only one of which is Slav, Moscow used to compare this policy to those famous Russian dolls, matryoshki  --  inside every majority, there's yet another minority  --  it was called 'matryoshka nationalism'.   Furthermore, when the first ethnic clashes took place in the Caucasus in August 1988, in Nagorno Karabakh, the headline in the state newspaper Pravda the next morning was, "This is our Northern Ireland," ("Vot, nash Ol'ster"  --  'Вот наш Ольстер').  Today however, in Ukraine, Putin does support referendums, sometimes, as in Crimea and Donetsk (and South Ossetia), when the results are what he had wanted... but not in Krasnoarmiisk, a part of Donetsk which voted by 69%, that's about 2 million voters, to opt out of Donetsk and opt back into Ukraine (Dnepropetrovsk).  In a nutshell, a majoritarian interpretation of the right of self-determination is wrong.

But the West's biggest error was in 1990/1, when we did not do business with him; after violence in (Georgia, Azerbaijan and) Lithuania, we ditched Gorbachev and supported the careerist Boris Yeltsin.  It was a huge mistake.  (And because the USSR was thought to be so similar to Yugoslavia, the West also decided to oppose the extremist Slobodan Milošević in Belgrade, and to back Franjo Tudjman in Zagreb instead, another extremist, swapping cancer for leukemia, to quote Bosnia's Alija Izetbegović.)  In pursuit of power, Yeltsin supported the break-up of the Soviet Union, but not the break-up of the Russian Federation: hence the first of two wars in Chechnya; hence Putin; and hence the current horror of war in Ukraine.