Now here's a convoluted tale for you...
Back in the early 90's a Miami entrepreneur named Vince Perri decided to get into the video game business. Specifically, he was inspired by one of his son's friends who owned a bootleg multi-cartrige with 52 games on it. He puts together a video game company called Active Enterprises Limited and got some guys with programming experience. He tells them to come up with 52 games to fill up the cartridge, and gave them six months to do it.
The result being the unmitigated disaster that was the Action 52 cartridge. Fifty two games, all of them buggy and unplayable.
The most famous of the games off the cart is the Cheetahmen. Active Enterprises intended them to be their Teenage Mutant Ninja Turtles, their flagship characters to be marketed for toys and cartoons. They were a trio of mutant cheetahs, turned into humanoids by a mad scientist who had the usual plans for global domination. The game and these characters have become a meme (the game's theme song surprisingly popular)
Now for the question of copyright. It seems Active Enterprises registered the Trademarks for Cheetahmen, but there's no records of a Copyright registration (but by the 90's that was not necessary was it?)
Active Enterprises folded within a few years after the games came out. Vince Perri clearly distanced himself from the company's failure, and has since died. In recent years, at least two different retro gaming groups have tried reviving the game with mixed results, but neither of them have any clear claim of copyright to the characters.
The game debuted in 1991, Active Enterprises folded sometime in 1994, and Vince Perri died in 2012. The copyright would still be in force, but it seems it has fallen into the category of orphaned work.