Good writers borrow, great ones steal. That is how the quote goes at the very least, and it has wisdom to it. I find the same is true for GMs as well, and everyone has their own sources of inspiration. So what is yours?
I'm not ashamed to say that over the past few years I have stolen a good amount of things from League of Legends. League has been a big part of my life - my free time anyhow - for the past several years, so obviously the exposure is there. Beyond that though, League has 115+ characters that have each been designed in such a way they could be a main hero or villain in a number of stories. The world itself is also interesting, and being more and more developed with every year.
Now, remember the quote. Good writers borrow. Great writers steal. The key here is to be stealing content, which means making it your own. You can't just lift a character you like and insert them into your game - well, you can but unless they're from that world it could feel awkward. However, you can take the character and make them your own. Take what you love about the character, change some of the details around that. Make the character your own, slap it into your game, and it will look like it belongs there.
Obviously if you take from something your players are familiar with they may recognize the source. But that's fine too. If you've done the work to make the character your own it can still surprise your players, and that's always fun.
So where do you take from? And how well has it worked?