Scooby-Doo
The first episode of "Scooby-Doo, Where Are You!" "What a Night for a Knight" debuted on the CBS network Saturday, September 13, 1969. The original voice cast featured veteran voice actor Don Messick as Scooby-Doo, radio DJ Casey Kasem (later host of radio's syndicated "American Top 40") as Shaggy, actor Frank Welker (later a veteran voice actor in his own right) as Fred, actress Nicole Jaffe as Velma, and musician Indira Stefanianna Christopherson as Daphne. Scooby's speech patterns closely resembled an earlier cartoon dog, Astro from "The Jetsons" (1962–63), also voiced by Messick. Seventeen episodes of "Scooby-Doo Where are You!" were produced in 1969–70. The series theme song was written by David Mook and Ben Raleigh, and performed by Larry Marks.
Scooby-Doo
Scheduled opposite another teenage mystery-solving show, ABC's "The Hardy Boys", "Scooby-Doo" became a ratings success, with Nielsen ratings reporting that as many as 65% of Saturday morning audiences were tuned in to CBS when "Scooby-Doo" was being broadcast. The show was renewed for a second season in 1970, for which eight episodes were produced. Seven of the second-season episodes featured chase sequences set to bubblegum pop songs recorded by Austin Roberts, who also re-recorded the theme song for this season. With Stefanianna Christopherson having married and retired from voice acting, Heather North assumed the role of Daphne, and would continue to voice the character until 1997.