Borrowing

Sometimes a writer admires a character written by another author that he wants to mention that character or make reference in his story. Perhaps you want to make a phrase like "As I waited for the light to change, I saw that scuffy detective talking to that famous police psychologist. The latter had not changed his raincoat for weeks." Pretty sneaky way to mention Columbo. You are not saying who he is, but anyone who watches the series knows who you are referring to.

Unfortunately your character would have no idea who that scuffy guy in the raincoat is. He would probably think he was a bum.

Now suppose you want your character to say that he saw Spiderman crawling up a wall. After all, you read that comic book and you saw this man poking out the apartment window, looking up.

If it were reality and Spiderman was crawling up a wall, your character may have seen it so many times that he would have not taken any notice.

All right, you decided to be bold and write a story about a widow of a police detective suspected of corruption asking a detective of a famous writer who lives in the same town as you to investigate. Now suppose it was in November 1998. Unfortunately the famous writer wrote a story of the same time period, but he had not sent it to the publisher yet. In this, the detective of the famous writer is in Ireland, investigating the mysterious death of a relative and he left in October 1988 and is spending the Christmas holidays there as well.

Not to be perturbed, you make your character be related to an action hero of another famous writer. This hero in the writer's last novel was getting close to a certain young lady and there were hints of marriage. Okay the writer may have intended to make the character married but his audience would not accept this for now. And for reality's sake, would not the hero's employer's order him to fake his wife or his own's death, make a different identity like he was in the import business, etc. And would not those who hired this action hero make sure that any real marriage of his was kept secret, perhaps a fake one in his place, along with a cover story? Why if your character was related to this borrowed character, he would probably think that his father was a business traveler, salesperson, et cetera. Why he may think his father died, divorced, or a bum who left mother and I penniless.

All right you decide to mention that your character was in the same area when something happened, perhaps the action hero was chasing someone (okay Chinese Communist agent) and there was a big fight. You decide to play safe by mentioning not the city or state but it was "near Macey's around Christmas 1985". You researched and know that the author wrote a story called, "Danger Christmas". But your character would probably have been approached by the government, CIA, or whomever hired the action hero to keep quiet in the interest of national security

The safest way to reference a borrowed character would be at a distance, a character who could be but you are not sure, mention being at a certain restaurant when the action hero was getting in trouble with the waiter - "I hope this is not what happened the last time I was here. The waiter seemed to be arguing with this customer. Who? I don't know. He looked like military or something.

This is probably the safest way to write about the danger of using characters borrowed from other authors than to say "You would violate copyright and you would probably not get the author's permission.