WWE Hall of Famer "Superstar" Billy Graham has died ... TMZ Sports has confirmed.

Billy's family tells us he died Wednesday after being taken off life support. We're told Billy's wife and daughter were by his side when he passed. As we reported, Billy's wife Valerie announced Monday he had been in the ICU for three weeks as a result of various health issues. She said doctors wanted to take Billy off life support Monday night, but she initially refused.

Known for his prowess as a wrestler and a bodybuilder, Billy rose to fame back in the day Wrestling for the American Wrestling Association and later the World Wrestling Federation.

Billy mentored big-time wrestlers like Hulk Hogan, Scott Steiner, Ric Flair and Jesse Ventura ... and in 2004 the WWE inducted Billy into its Hall of Fame.

Billy's recent health issues took a toll on his body ... his family says he lost 45 pounds while suffering from congestive heart failure, diabetes, hearing loss, and a significant infection in his ears and skull. We're also told his kidneys were failing.

Tributes are now pouring in from across the wrestling world ... with Ric tweeting, "THANK YOU FOR ALL YOUR INFLUENCE On My Career!"

Billy was 79.