The ongoing confiscation of Copyright law by the big media corporations so infuriates me that I could rant forever. Luckily for you I won't. Here's the short version.
I'm not a scholar of copyright law, but I've read much about its origins. What has been happening here in the US (and in other countries with powerful media monopolies) is a 180-degree about-face in the understanding of what copyright is for. In the 18th century when all this began the underlying assumption was that EVERYTHING would--even should--eventually be in the public domain. Copyright laws basically rewarded a creator for his effort by giving him a head start. He got to profit off his creation for a certain period, after which it would become part of collective public knowledge and anyone could build upon it. Of course changes in technology and business models began warping this notion almost immediately. Once it was clear a lot of money was to be made off books, phonograph records, sheet music, etc. all manner of tricks (like work-for-hire) were devised to extract as much money as possible for as long a period as possible with as little hassle as possible.
Over the last several decades, as profits from media and music have grown into the trillions of dollars, the big media corporations have been reshaping copyright with the intent that NOTHING should ever be in the public domain. One of the pioneers of this destructive legislation was Sonny Bono, of Sonny and Cher (in)fame, who got into the California legislature and began pushing laws on behalf of his buddies in the record industry. These laws set the stage for today's abusive "intellectual property" constructs, in which big corporations get to milk forever content they had nothing to do with creating. Music is the poster child of this change, as Nina Paley discovered when she made "Sita Sings the Blues." A corporation can claim "ownership" of a property whose writers, musicians, producers, recording engineers, you name it, are long dead and to which the corporation had no connection whatever except the ability to buy "rights" to the work and control it forever. Recent legislation has been even been working to RE-COPYRIGHT ITEMS ALREADY IN PUBLIC DOMAIN, which is anathema not only to common sense but to legal precedent.
Here's why this is relevant to this discussion. A corporation with enough money can claim almost anything, regardless of the fine points of the law, and defend it against objectors either by bleeding them dry with legal fees or by buying court judgements that hit the objectors with fees and fines to be paid under penalty of jail time. By all rights Mickey Mouse should be in the public domain by now. But you can bet your mouse ears he will NEVER be anything of the sort. Nor will Marvel or DC characters.
What hasn't happened so far is a corporation staking out a public domain character and claiming ownership. I suspect it's only because most PD characters aren't likely to make them money. As jimmm points out, comic characters have been stealing from each other for generations, so most PD characters are variations of established characters with greater name value. But let's suppose DC wanted to revive--I don't know,. let's say The Bouncer. They put out a Bouncer comic, make a Bouncer movie, and say, "We own The Bouncer!" But publisher Guyserman says, "The Bouncer is public domain!" and puts out a Bouncer comic. DC says, "Cease and desist, damages, plus you pay our legal fees at $1000 an hour." The appellate court says, "Yassuh mistuh DC Boss, yo' sho' nuff right!" and once more the sacrosanct Law is upheld.
The final affront is that all this is presented under the guise of "creators' rights." A few very successful musicians stand up and agree: misuse of intellectual property hurts us terribly! Of course they agree--they're rich corporations too and probably own a library of lucrative "intellectual properties." But they, and the content corporations, don't give a hang about run-of-the-mill creators. They'll do everything they can to remove said creators from the pipeline ASAP so they can get on with the business of owning all the marbles. That's why it's so useful to control works by dead creators. And why it's beneficial to do sequels and re-hashes of already-owned properties. The less money and time put into content creation, the greater the margin, the quicker the profit, and the easier the management of the all-powerful "rights."