Just when you thought Scooby-Doo had solved his last case, consigned to an eternity of syndicated reruns, ABC decided to bring Scooby back after a 2 year absence in 1988. This time, however, there were a few changes.
A Pup Named Scooby-Doo was Hanna-Barbera's 2nd series in which they had rebooted iconic characters by focusing on their younger years (Flintstone Kids came 2 years earlier, ironically replacing Scooby on the schedule). Pup lasted three seasons, but was kept around in repeats, according to Wikipedia, until 1993, at which point ABC bade their final farewell to Scooby, who had been a fixture on Saturdays on the network since moving to CBS in 1976, save for that two year vacation (1986-88).
Pup marked the first time that Casey Kasem (Shaggy) & Don Messick (Scooby) were given top billing, and would be the last time that Messick would be the voice of Scooby. Messick passed away before production began on the first of the Scooby DTV movies, "Scooby-Doo on Zombie Island", which was released in 1998. Actress Kellie Martin, later of Life Goes On & E R, voiced the younger Daphne, who was shown to be rather wealthy, something that had not been fully explored in earlier series.
Some believe that Cartoon Network's live-action Scooby prequels have retconned Pup out of existence, but that is left open to debate. Here's the open to Pup:
Producer Tom Ruegger also worked on 1985's 13 Ghosts of Scooby-Doo, but is better known for spearheading the revival of WB's animation division in the 90's.