Ben's wife, actress Ilene Graff tells TMZ ... Ben passed away peacefully in his sleep Friday after a battle with lung cancer.

Graff says she was with Ben -- to whom she was married for more than 45 years -- when he died.

While many people might not know Ben's name, they definitely know the music he helped create ... with his work appearing in many iconic shows from the '70s,'80s & '90s.

Among them ... "The Love Boat," "Happy Days," "Dynasty," "Mork and Mindy," "Laverne and Shirley," "The Tracey Ullman Show," "The Colbys," and "Mr. Belevdere."

Ben and Ilene met on the set of "Grease" -- where Ben worked on the music video for "Summer Nights" -- and later worked together on 'Belvedere' where Ilene played Marsha Cameron Owens for 118 episodes.

Ben was honored with the ASCAP's Most Performed Underscore Award in 1986 and is survived by Ilene and his daughter Nikka.

Ben was 85.