Keep in mind that you cannot copyright ideas. You copyright the specific implementation of those ideas. So simply mentioning Zaphod Beeblebrox doesn’t trigger anything to do with copyright, but if you had a word for word introduction of Zaphod Beeblebrox copied straight from Hitchhiker’s Guide that would be a problem.
Then after that you can normally have “de minimus” use, where you can use a small portion (think quotes, short phrases etc). As long as your work can’t be used as a replacement for the original then you are normally in the clear (legally speaking, as far as copyright goes).
But none of this goes into trademark law, but that’s a whole other thing and are generally easier to avoid too (e.g. don’t use the word “coke” to sell your drink).
TL;DR: As long as the AI doesnt spit out a verbatim copy of the original, and then if you copied it verbatim from the AI, then you’d be in trouble.
I am not a lawyer, just a dude interested in copyright law.