For the vast majority of IP out there (that’s “Intellectual Property” to the layman), the ownership is pretty clear. It defaults to the person who created it, unless they are working for a company employing them to create it, in which case it usually belongs to the company. The person or company who owns a particular IP but wants to let others use it can either sell the IP outright, or grant third parties a license to use the IP under specific conditions. Most of the time, these work out fine for all parties involved. If enough time has passed, then the IP falls into public domain, in which anyone is free to use or distribute it as they see fit (though with companies like Disney pushing Congress to perpetually extend copyright protection, who knows if anything from the last 75 years will ever make it).
Sometimes, however, things get a little more tangled. Sometimes ownership of the IP is disputed between two or more parties; other times, an owner and a licensee have a falling-out and can’t agree on distribution terms of extant materials. Once in a great while, no one knows who has the rights and it’s not worth the time and effort to make a legal determination.
For whatever reason, some stories, movies, books, or other forms of IP exist that can no longer be redistributed, built upon, or otherwise commercialized, and those who want to consume it are stuck with second-hand media or fan-generated knockoffs.
Today we mourn our favorite stories, books, movies, characters, and other IP lost to legal limbo.