Yandex.ru is the most popular in Russia. According to the official stats this company has 64% of market share in that country!
I used to work for a Russian company which was a nightmare as I am English - we managed to work around Yandex - it's amazing why it's so popular the algorithm is very much out dated. I prefer Rambler
In most of the countries Yandex is famous search engine.I show you one pictures which show you, In which contries Yandex is most famous as compared to others. http://webempires.org/wp-content/uploads/dominating_websites.jpg
Yandex is the most popular search engine in Russia. About 49,46% people of Russia use this search engine.