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Christopher Dennis -- a street performer known for portraying Superman on Hollywood Blvd. for more than 25 years -- has died ... TMZ has learned.

Law enforcement sources tell us ... Dennis was found dead Saturday in the San Fernando Valley. We're told his body was discovered lying headfirst in a bin that's used for clothing donations.

Investigators believe Christopher -- who was homeless -- was attempting to gather clothes for himself. Our sources say no foul play is suspected.

Dennis' story is both charming and tragic -- after 2 decades of entertaining folks in Hollywood by impersonating The Man of Steel, he was the victim of a vicious assault and robbery that nearly killed him and left him without a way to make money.

He was rendered homeless, but thanks to the help of friends and a Kickstarter campaign, he got a new suit that allowed him to get back on his feet ... and return to the Blvd for the Superman fans.

He also starred in the documentary, "Confessions of a Superhero," and appeared multiple times on "Jimmy Kimmel Live!"

Sadly, it seems he fell on hard times again recently.

Christopher was 52.