@PotomacBob
Who can explain the difference between copyright and trademark in terms so simple that even I can understand the explanation?
In short, it's the difference between the work as published and the name or characters. This can really be seen when dealing with works that have fallen into the public domain.
Case in point, the original version of Betty Boop is now in the public domain, as is the first four Nancy Drew novels. Anybody can now use those characters and setting for free as much as they want.
However, that only applies to those works from 1930. And those versions of the characters are not the same ones that most are familiar with. You are free to use Betty Boop as much as you want, but only the 1930 version where she was still a dog. And only the original 1930 Nancy Drew, not the character that was rewritten or morphed over the decades.
You can even use "Pluto" from Disney, but you have to call him "Rover" and have him owned by Minnie and not Micky.
And in short, those either exist for 95 years, the lifespan of the creator plus 70 years, or so long as they continue to use it.
These areas have actually become increasingly muddy as when the legal concepts were originally created, nobody had expected media to still be created based on such things over a century after they were created.