The U.S. imposed sanctions on a number of Russian President Vladimir Putin's close associates and alleged business partners in his inner circle, but the highest-profile target is oil billionaire Gennady Timchenko.

On Wednesday, the U.S. banned Timchenko and 19 others from entering the U.S., from doing business with U.S. companies or financial institutions, and assets they own in the U.S. were frozen.

Here are 10 things to know about the billionaire businessman:

1. Timchenko was born on Nov. 9, 1952 in Leninakan (now Gyumri), Armenian SSR, about 750 miles from Crimea. His father served in an unknown rank in the Soviet military, and Timchenko spent part of his childhood in the German Democratic Republic and in the Ukraine.

2. He was ranked 61st on Forbes magazine’s 2014 world billionaires list, with a net worth of $15.3 billion. His net worth was estimated in 2008 at $2.5 billion and at $400 million in 2009.

3. He was ranked as the sixth-richest Russian in 2014.

4. Timchenko co-founded privately held Gunvor Group Ltd. in 1997, which is now the fourth-largest oil trader in the world. The U.S. Treasury alleges that Putin has investments in Gunvor and may have access to Gunvor funds. The Kremlin denies the allegation.

5. Timchenko, until Wednesday, owned a 45 percent stake in Gunvor, his largest asset. But immediately after the U.S. and the EU imposed sanctions, he sold his shares to his co-founding partner, Torbjorn Tornqvist.

6. Timchenko also has stakes in Novatek, Russia’s second-largest gas producer behind state-controlled Gazprom, and Sibur, Russia’s largest petrochemical manufacturer.

7. In addition to Russia, Timchenko also has citizenship in Armenia and Finland, which makes him a European Union national. He lives in Geneva with his wife, Elena, and their three children.

8. Timchenko graduated in 1976 from the Mechanical Institute of St. Petersburg (then Leningrad) as an electrical mechanical engineer.

9. Timchenko, along with other associates who were sanctioned this week, co-founded in 1998 a club for judo, a sport Putin enjoys.

10. Timchenko became a leader in the Russian oil trading industry in the 1980s when he helped set up export routes for oil products from the USSR to western countries.