As far as actors who pop up again and again in Japanese dubs, and because they're really good actors, people like Steve Bloom, not only in 'Cowboy Bebop,' but also he's sort of the de-facto Wolverine. If you're doing an animated Wolverine anything, Marvel usually just goes to Steve first because he's recognized as that voice.
It usually starts with the director and any other creatives who may be involved at the start. It's a collaboration. I bring what I have naturally and, hopefully, what they cast me for, and then we start playing and tweaking until we have what they feel's right. It helps to have some artwork to inspire me, but I don't always get that luxury.