I've seen these kind of character sketch sets done for a number of different kinds of characters. For my Ultrahuman books, I decided that I'd do them for the principle characters since, in a superhero setting, the costumes are important and I wanted to have all the details right when I was describing them. So I do, front, side, and back views, plus an 'action shot' of some sort. In this case the action shot came in useful since it shows the rope-dart which is Mink's signature weapon.
Mink is a semi-new character for the third book (she got mentioned in the second, but never appeared). She's one of San Francisco's resident Ultras (in-world name for super-hero types). This is about the sixth costume variation I've been through with her, and it's the one I'm most happy with. Most of the previous ones had a lot of black, but then I went and checked, and mink are brown, and this chocolate synthetic material shader just looks awesome against her skin. Going brown was a great idea, if I do say so myself.
Technical stuff: This is a pure IRay render done in DAZ Studio with two mesh lights, and without any postwork. It was an 8 hour render and it still only managed something like 10% convergence, but the quality is quite good enough for my needs and I can't see any rendering artefacts that bother me.