The Lawnmower Man is both the winner, and kind of cheating as an answer.

The studio had an existing script called Cyber God that they had been sitting on for a while. When they finally got around to making the movie, they figured if they could stick Stephen King’s name on it, then they might get more people to come see it. So they went out and bought the rights to a random King story called The Lawnmower Man and then changed the title character’s job in their movie from janitor to gardener so he could use a lawnmower at least once.

King actually sued them in order to get his name removed from the movie and won. Then they put it back on for the VHS release anyway.

So it kind of hads to be the worst adaptation because it’s not even an adaptation at all. But also cheating a bit because not really an adaptation.

He does a lot of both.

Sam Fisher only does one.

I was into Tom Clancy books as a teenager. My mom bought me a book for Christmas that said in big letters across the top: “Tom Clancy’s Splinter Cell” and then much smaller at the bottom was a different author’s name.

For anyone not familiar, Splinter Cell was, for a while, a very popular and successful video game franchise that had Tom Clancy’s name on it as it was a spinoff of the Rainbow Six series which was based on one of his books. Tom had almost (completely?) nothing to do with the Splinter Cell series though. The company just had permission to put his name on it and the full title of the series was usually presented as “Tom Clancy’s Splinter Cell”. Along with that, someone decided a good cash in might be to put out some novels with the game’s protagonist as the main character. They stuck Tom’s name real big at the top and mostly his the actual author’s name (pseudonym) on the bottom hoping to fool some folks. Worked on my mom.

It wasn’t a long book, so I read it anyway. Awful. Basically knock off shitty James Bond with a very obvious “reveal” that anyone should see coming a mile away. Which is extra dumb because the character from the game is much more John Wick than James Bond. He doesn’t go under cover and hit on ladies, he sneaks into buildings and shoots people. They wrote him as much more dull Bond instead though. Also, extended sex scene for protagonists teenage daughter for no particular reason.