You might say it was viewer demand that brought Jonny Quest back for all-new adventures as part of the Funtastic World of Hanna-Barbera in 1986. Edited repeats of the original 1964 series were back in syndication at this point in some cities, and interest was such that Jonny would eventually be licensed to Comico for a comic book series that lasted about as long as the TV revival did, if not longer.
Only 1 season of new episodes were produced, and only Don Messick (Dr. Benton Quest/Bandit) returned from the earlier series. Messick, in fact, had taken over for John Stephenson as Dr. Quest six weeks into the original series. Lord only knows what brought that change on. Scott Menville landed one of his first lead roles as Jonny, who sounds much younger than he did in the original as a result.
2 TV-movies would follow, with the first, "Jonny's Golden Quest", premiering on USA Network, if memory serves. The 2nd one, "Jonny Quest & the Cyber-Insects", would make its debut on TNT, and not long after, a new series, The Real Adventures of Jonny Quest, surfaced on Cartoon Network as part of its then-weekday Toonami package. Jonny & Hadji were allowed to age just a tad, and Race Bannon's daughter, Jessie, was added to the mix, allowing the producers to tease the prospect of either of the boys falling for Jessie. Didn't happen, unfortunately. Real Adventures, however, was fraught with more casting changes, as they ended up using 2 actors apiece for each of the core characters. We'll discuss that another time.
What was missing from the 1996 series and the 2 TV-movies, though, was the subject of the episode, "The Monolith Man", Hardrock (Jeffrey Tambor, ex-The Ropers), who would remain for the final 5 episodes of the 1986 series, and was never seen again. We won't see Hardrock, though, in this sample.
Not long ago, some jabroni came up with the idea of a live-action adaptation of the series, with Zac Efron as Jonny. Luckily for us, it never got past the talking stages.