Jared Harris (Mad Men, Fringe) has been cast as Holmes rival Professor Moriarty in Sherlock Holmes 2, according to Variety.  The character was introduced in the first film, but the character’s appearance was not shown. 

Harris joins the recently announced Stephen Fry (cast as Holmes’ brother, see “Stephen Fry to Play Mycroft Holmes”), Robert Downey, Jr., Jude Law, and Noomi Rapace in the Guy Ritchie-helmed film.