As O’Neill had hoped, Disney sued him for copyright infringement. He believed it was legal parody. But after 8 years in court, he was saddled with a judgment he could not pay. To stay out of prison, he agreed never to draw Mickey Mouse again.

“It’s still a crime for me,” said O’Neill, 81, from Nevada City, California. “If I draw a picture of Mickey Mouse, I owe Walt Disney a $190,000 fine, $10,000 more for legal fees, and a year in prison.”

Mickey Mouse has long been a symbol in the copyright wars. Beyond the practical impact, the expiration — 95 years after his debut in the short film “Steamboat Willie” — is also a major symbolic milestone.

“This is a big one,” said Jennifer Jenkins, director of Duke Center for the Study of the Public Domain. “It’s generating so much excitement in the copyright community — it’s finally happening.”

After Congress extended copyright terms in 1998, 20 years went by when nothing entered the public domain. Works began to lose copyright protection again in 2019, and since then, it’s been open season on “The Great Gatsby,” “Rhapsody in Blue” and Winnie the Pooh.

The recent adaptations of those works could offer a preview of what awaits Mickey Mouse.

“‘Just add zombies’ appears to be a popular thing to do,” Jenkins said.

“The Great Gatsby Undead” popped up on Amazon on Jan. 2, 2021, followed by “The Great Gatsby and the Zombies.”

There is also “Winnie the Pooh: Blood and Honey,” the slasher film that made several critics’ lists of the worst films of 2023. Released in the U.S. in February through Fathom Events, the film commanded attention for its shock value but to date has grossed only $5 million worldwide.

Lessig may be as responsible as anyone for putting Mickey Mouse at the center of the copyright debate. He was the most prominent critic of the 20-year extension, without which Disney’s copyright on its signature character would have expired in 2004.

Lessig called the law “the Mickey Mouse Protection Act.” He does not remember whether he coined the term or borrowed it from someone else, but he used it a lot, and it stuck.

Disney certainly lobbied for the bill. But some argue that its role in the legislation has been exaggerated, noting that many other copyright holders — including songwriters and the George Gershwin estate — also pushed for it.

“Disney’s fearsome reputation was always a little overstated. They make a convenient bogeyman,” said Zvi Rosen, a law professor at Southern Illinois University who argues that Disney’s lobbying was not a major factor. “It became really about Mickey Mouse in terms of the public debate once the law was passed.”

“That movement awoke people to the essential need for balance in this,” Lessig said. “At the beginning of this fight, it was a simple battle between the pirates and the property owners. And by the end of that period, people recognized that there’s a much wider range of interests that were involved here, like education and access to knowledge.”

As the clock began to wind down on the extension in the 2010s, some anticipated that Disney and other copyright holders would push for another one. But that never materialized.

Some argue that copyright holders recognized that another extension would face a storm of protest, and so they didn’t try. At some point, it became clear that Mickey Mouse really would fall into the public domain.

“It’s significant,” Lessig said. “Let’s hope it’s the opening of a new chapter.”

He continues to support reforms that would free up a vast body of cultural output that remains inaccessible because it lacks commercial value and its ownership cannot be determined.

“The biggest weakness in copyright is that we have no way to know who owns what,” Lessig said. “It’s the most inefficient property system known to man.”

Disney will still have ways to protect Mickey Mouse after Jan. 1. The company will retain copyrights in the character’s more modern versions for a few more years. And it has said that it will continue to defend its trademarks, which could limit what creators are able to do.

“This is very different than Winnie the Pooh,” said Justin Hughes, a professor who specializes in intellectual property at Loyola Law School. “When Winnie the Pooh fell into the public domain, you could have ‘Winnie the Pooh: Blood and Honey.’”

“There will be some legitimate public domain uses,” Hughes said. “But people will have to be very careful that they don’t trigger a legitimate trademark claim by Disney.”

Jenkins, however, rejects the idea that Disney can use trademark law to shut down creative expression. Trademarks are intended to protect brands. So long as artists do not try to pass off their work as coming from Disney, she said, they should not have a trademark issue.

Rosen said it may take litigation to settle the issue.

“Someone is going to make something Disney has to sue over,” he said. “It’s almost inevitable.”

Disney’s reputation for zealous copyright enforcement goes back decades, at least to the “Air Pirates” case. It was cemented by two incidents in 1989. First, Disney sued the Oscars for unauthorized portrayal of Snow White. Then, it demanded the removal of murals featuring Disney characters from the walls of three day-care centers in Hallandale, Fla.