Because they are fun, that’s why. The latest one, just finished today, is Iron Man: Virus. I had a good time working with Tony in the Ultimates book I wrote a couple of years back, so it was good to get reacquainted with him (although his non-Ultimate self is markedly different in some ways). Plus how can you not love a chance to involve HYDRA and a certain body-hopping villain named after a French novelist? It comes out at the end of January, 2010, in case you want to plan ahead.