My favorite unenforced instance of copyright infringement stems from David Bowie’s song Space Oddity. (Before we continue, yes, some lawyers have favorite instances of unenforced copyright infringement.)
Space Oddity debuted in 1969, just nine days before Armstrong and Aldrin landed on the moon, while Michael Collins orbited above them. While the actual astronauts were safely returned to Earth, the fate of Major Tom was left…up on the air.
In 1980, David Bowie released Ashes to Ashes, which revisited Major Tom, implying that he returned to Earth and has since become a junky. Major Tom was also the focus of later Bowie songs Hallo Spaceboy and arguably in the recent Blackstar
In 1983, Peter Shilling retold the story of Major Tom with a happier ending. But that character is owned by David Bowie, and “Major Tom (Coming Home)” is at least arguably an unauthorized derivative work.
Because a copyright comes with the exclusive right to make derivative works (sequels, alternate retellings, or copies of the work in other media), Peter Shilling is arguably infringing David Bowie’s copyright by making unauthorized use of the character of Major Tom.
It’s also arguably a fair use of the original material, but that’s much less amusing.