Boris Yeltsin was President of Russia between July 1991 and the end of 1999 – initially with Russia still being a constituent republic of the USSR, but for most of that time with Russia being “on its own” as a country. He was instrumental in the collapse of the USSR and the destruction of Russia’s standard of living in the 1990s.
He is known for the “economic shock therapy” he imposed on Russia in order to convert it from a centrally-planned state capitalist regime to a neoliberal market economy, complete with massive privatisations that enriched a tiny number of oligarchs at the expense of everyone else. He eliminated subsidies, wrecked Russia’s welfare system, and presided over sky-high inflation that eliminated the savings of most people who had any. Russia’s GDP fell by 50% over his time in office, with widespread unemployment and high wealth inequality – an estimated 50% of Russians were living below the hunger line at one point. Corruption under his regime was rampant. Many Russians emigrated.
He also presided over three wars – two in Chechnya, and one in Dagestan.
Yeltsin resigned at the end of 1999, leaving the leadership to his chosen successor, Vladimir Putin. By that time, he had an approval rating of 2%. American politicians remember him fondly for destroying their Cold War enemy (his own country) more effectively than they ever could; Russians largely hate him.