His onetime ring partner, The Iron Sheik -- with whom he won WrestleMania I's World Tag Team Championship in '85 -- confirmed in a tweet Sunday that Volkoff had passed away.

Volkoff, who's real name was Josip Nikolai Peruzović, wrestled in the WWWF from 1968 to 1971 where he won a tag team title in 1970. After that, he went on to wrestle singles ... and later returned to the WWWF between '74 and '80 and then again for a second time in '84.

Volkoff had a successful run teaming up with Sheik in multiple wrestling events between '84 and '87 as well as other wrestlers in the years after. He went back and forth between foreign heel and hero through the '90s and eventually scaled back wrestling through the 2000s ... although he did make appearances in WWE.

Although he was Croatian, Volkoff was portrayed as a Russian ... and would often rile up the crowd by singing the Russian National Anthem.

WWE released a statement on Volkoff's passing, saying in part ... "As one of the greatest villains sports-entertainment had ever seen, Volkoff’s infamous rendition of the Soviet National Anthem before his matches made him an instant icon in the eyes of the WWE Universe as a Superstar they truly loved to hate ... WWE extends its condolences to Peruzović’s family, friends and fans."

Volkoff was inducted into the WWE's Hall of Fame in 2005. He was 70 years old.