US outlet Variety said Ruby died of natural causes on Wednesday in Westlake Village, California.
“He never stopped writing and creating, even as he aged,” his grandson, Benjamin Ruby, said.
Ruby was a writer at cartoon powerhouse Hanna-Barbera when he teamed up with Ken Spears to create the mystery children’s cartoon Scooby-Doo, Where Are You!
The cowardly but lovable Great Dane made his debut in 1969, with all but four of the first 25 episodes written and story-edited by Ruby and Spears.
Scooby-Doo has proven to be an enduring staple of children’s cartoons and the character has featured in multiple TV series and films, most recently the computer-animated film Scoob! in May.
As well as Scooby-Doo, Ruby and Spears, 82, also created the characters Dynomutt, Dog Wonder and Jabberjaw at Hanna-Barbera.