The New York Times has an obit. Found out via Fred Pohl. I read some of Harrison's work, but probably most memorable to me was the series which began with Hammer and Cross series in particular captured my imagination. With hindsight it's pretty obviously an inversion of Christian fantasy in more than just the plain sense. Where in much of Christian fantasy the revelation of the religious truths bleed into the story through a process of unfolding, Harrison's rather conventional anti-Christianity is firmed up by an alternative and utopian vision of the early Middle Ages.