One of Ukraine's Olympic heroes is putting on his cape again by sacrificing his gymnastic silver medal in order to help his country fend off the Russian invaders.
Ruslan Mezentsev put his medal -- earned during the 2000 Olympic Games in Sydney -- on the auction block, and TMZ Sports has learned it's now sold for $14,438.
Bidding just ended on July 21, and as we first reported ... Ruslan had pledged to donate all the money to Ukraine, to help fund his homeland's war efforts against Russia.