Scooby doo full episodes free , Where Are You! ” What a Night for a Knight ” appeared on the CBS arrange Saturday, September 13, 1969. The first voice cast highlighted veteran voice performing artist Don Messick as Scooby-Doo, radio DJ Casey Kate (later host of radio’s syndicated American Top 40) as Shaggy, on-screen character Frank Welker (later a veteran voice on-screen character in his own right)