The martial arts world has lost a legend ... Toshihiko Koga -- who won a gold medal at the 1992 Barcelona Olympics -- died at 53 years old Wednesday, officials in Japan confirmed.
The judo champ -- a 3-time Olympian -- had reportedly battled cancer in the past year ... though it's unclear if that was the cause of his tragic death.
Japanese politician Katsunobu Kato lamented the loss of Koga at news conference Wednesday ... telling reporters, "He was so young, and the news of his death is such a shame."
"I express my deepest condolences.