Vicinanza, along with Hollywood-based partner Vince Gerardis (who also shared a co-executive producer credit), ran the Created By management and production company which represents the film and television rights for most of the notable names in science fiction and fantasy, both past and present (among them are Stephen King, Larry Niven, Robin Hobb, Joe Haldeman, Isaac Asimov, and of course George R.R. Martin). It seems clear from the co-executive producer credit that Created By had a direct hand in bringing Game of Thrones to television. They are specifically mentioned by Martin when he first announced the HBO option on the series way back at the start of 2007.
Vicinanza had recently expanded his involvement from simply representing to having a more direct hand in developing projects, with his most notable other credit being one of the executive producers of FlashForward, which was based on Robert J. Sawyer’s novel of the same name. However, our understanding of Vicinanza’s co-executive producer status on Game of Throneswas that it was more a notional than a working position, and that his day-to-day involvement in the series was substantially less than GRRM’s.
Our condolences go out to his friends and family. A memorial service is planned on October 1st.