Vladimir Putin
According to the Constitution of Russia, no-one can be president three times in a row. Because of this, Putin didn't put himself forward for the March 2008 election. However, you're allowed to be president as many times as you want, as long as it's not for more than two times in a row. In March 2012, Putin put himself forward for the elections, and won 64% of the vote. This means that he was the president of Russia until 2018.