"All of the stuff I can't afford to do on a TV budget, I just put into the comic book because you're ..." — Marc Guggenheim

Fortunately, the DC Universe is full enough and replete enough with every kind of character that you could want, that it's not that hard to find the right character. Sometimes it's nothing more than an Easter egg, or a name drop, and sometimes it's someone like 'Deathstroke,' who is a huge part of the DC Universe.