Boris emerged as a hero in August 1991 when he helped stop a coup attempt in Moscow, and won support from the USA and Europe when he vowed to bring capitalism and democracy to Russia. At the time Russia was very optimistic and glad to see the back of the Communist regime, but they were soon dissapointed.
The 1990s were a very bumpy ride for Russia. Millions of Russians lost money, savings and jobs due to economic collapse and inflation, and as a result Yeltsin never won back his popularity. A few people benefited - the "oligarchs", a powerful group of billionaries who profitted from the privatisation of the economy.
Yeltsin was dubbed a "Democrator" because of his behaviour. He played by the rules of democracy and won a legitimate reelection in 1996. But some of his actions, like the war in Chechnya and the shelling of the Parliament building in 1993 were hardly democratic.
He resigned on New Years Eve 1999 and handed over his power to Vladimir Putin, the last of Yeltsin's long line of Prime Ministers. By this time, Yeltsin was so unpopular that his approval ratings were just 2%.
Not to mention of course, he often took to the vodka.