Professional writers more often than not find themselves writing somebody else's story or characters. There seems to be a collective perception that three in five films are adaptations, screenplays based on material from another source - books, plays, graphic novels, computer games, short stories, etc. I don't know how accurate that is, but the adapted screenplay category is always far more competitive at the Oscars.
When it comes to TV drama, the number of writers who only work on their own stories and characters is tiny. Scribes at the start of their careers can expect to pour their creative energies into pre-created shows. Continuing drama gives a lot of writers that vital gateway, a place to hone their skills while learning on the job. Few and far between is the emerging scribe who only writes their own inventions.
Computer games are even more prescriptive. Unless you own the computer or are a senior developer, you'll almost never get to create a game from scratch. Franchises and licensed properties dominate the market, all new games are the rarest of the rare. With millions of pounds and years of development work at stake, few companies will take a punt on your bright idea, no matter how great it might be.
Novels are perhaps the last great bastion of the originating writer, especially near the start of their career. You can invent a world, populate it with your characters and - with talent, luck and persistance - get it published. Your ideas, your tales, the offspring of your imagination all get transmitted direct into the minds of readers via ink on some pieces of dead tree [or pixels on an e-reader screen].
But even in book publishing, there's money to be made writing other people's characters and stories. You can novelise film screenplays or episodes from popular TV series, or create original stories based on characters and concepts from other storytelling media such as computer games, comics, TV dramas or role playing games. For many authors, this route offers their first chance of publication.
So here's a couple of guidelines for how to behave if you find yourself in any of the situations were you're temporary custodian of somebody else's story or characters. First off, don't break them. Best to think of your task as being invited to play with somebody else's toys or to drive their car. You're borrowing this, it's precious to them, so try to treat it with some car, okay?
Secondly, remember who's in charge. You own nothing in this equation, except whatever ideas and characters you've brought to the table. [In some fields, you won't even retain ownership of them - read your contract careful!] You are expendable, an ink-slinger for hire. That means you can be dumped as quickly as you got hired, and it'll probably happen quicker. So don't get too comfortable.
Thirdly, listen and learn. Do a good job and you might be invited back for another play with their toys. Bear in mind what you get out of the deal - payment, experience, a credit and the opportunity to learn. Plus you'll work with or for people who could be helpful to you in future at other places. All of these industries are small and word gets round, so play nice with the other kids.
Last, but certainly not least, respect yourself and your talent. If you feel you're being treated bady or exploited, you can always walk away, Renee. Yes, you may well be sacrificing money and it could lead to bad feelings. But if somebody's treating you like crap, chances are you don't want to work for that person again [or for somebody who employs them]. Take responsibility for yourself. Right - onwards!