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.
Scrappy-Doo
In "Scooby-Doo Meets the Boo Brothers", "Scooby-Doo and the Ghoul School", and "Scooby-Doo and the Reluctant Werewolf", Scrappy is more toned down, as he is less feisty and a little more cowardly, but still much braver than Scooby and Shaggy. In all three movies, he sometimes serves as the brains of the trio, figuring out the clues and where to go next. Also, the idea of Scrappy actually may not have been all that new to the series, as he "...bore a resemblance to Spears's and Ruby's initial idea for a feisty little dog", which was one of the early ideas for the Scooby-Doo character himself, along with the "big cowardly dog" ultimately chosen. Hints of Scrappy can also be seen in the fact that there were originally six members of mystery inc planned-Mike, Linda, Kelly, Geoff, W.W, and Too Much.It is unknown if one of the personalities was analogous to Scrappy, or which one it would have been.