The "little green men" in Ukraine
A bit gruesome, but such is the nature of war. The dead man is dressed in Russian army uniform, and his passport identifies him as a citizen of the Russian Federation that Vladimir Putin is busily expanding to the west. He was a Cossack, or anyhow a member of a Cossack unit, and a volunteer or professional soldier in the Russian army. (About half of Russia's 400,000 ground troops are conscripts, who are not required to serve in Ukraine.)
With all the lies and disinformation that come out of Moscow, and which are given too much credence by Western media, the facts are hard to pin down. It seems that 9,000 Russian troops are serving in Ukraine as fighters or advisers to the separatists (who themselves are largely creations of Moscow).