Doesn't have the rights any more, either. You know, in Star Wars folklore, one of the reasons Lucas wrote his own version of a 30's serial space opera was that he couldn't get all the rights to Flash Gordon or Buck Rogers, then realized that not only was creating an original property cheaper, but then all the machinery of copyrights and residuals, etc. would work for HIM, instead of someone else's estate.
Something similar happened with Jonny Quest. They were originally pitching an animated series based on the long-running popular radio serial:: "Jack Armstrong, The All-American Boy". They even shot test footage for the studio pitch. You see that test footage re-cycled in the titles sequence for Jonny Quest, in the scene where angry African tribesmen chase the hover-saucer-riding adventurers back to their swoopy-winged jet, which makes a hasty take-off.
Look closely at the initials on the tail: you ASSUME they read "J.Q"., but they really say J.A. for Jack Armstrong.