Sarris was specifically a champion of French "auteur theory," which, as explained in The New York Times' obituary by Michael Powell, posited that "a great director speaks through his films no less than a master novelist speaks through his books." Essentially Sarris and his ilk were responsible for ennobling American cinema to a previously unseen level, changing perception of the medium from being mere commercial entertainment to true art. A biting and at times downright bitchy writer, Sarris sparred with many of his contemporaries, perhaps none more so than the late, great Pauline Kael.
Kael, whose reviews for The New Yorker have been amassed in popular compendiums like I Lost It At the Movies and Kiss Kiss Bang Bang, rejected auteur theory as something male-focused and distracting. She and Sarris were of such differing views on how to analytically approach film, and they spoke their cases so smartly and vociferously, that they earned themselves warring legions of followers, cineastes who we might these days call, say, AV Club commenters. Indeed the Sarris/Kael wars represent an elegant, pre-Internet time for criticism and cultural commentary. Sure, the voices and opinions were perhaps more monolithic, outlets were limited after all, but the arguments made were always carefully considered and expertly crafted. Sarris, who was phased out of the Observer three years ago, was something of an admirable curio in the era of the Internet, a critic who didn't simply dash out a reaction in the quest for primacy.
Sarris wrote a heartfelt but not sentimental remembrance of his great nemesis Kael when she died in 2001, eerily, well eerily today anyway, doing some imagining about his own death. In addition to his criticism, Sarris taught film at Columbia University and was the author of several books, including The American Cinema: Directors and Directions 1929-1968 and The Primal Screen: A History of Science Fiction Film. He was married to the film critic Molly Haskell, who also teaches at Columbia and wrote for a time at The Village Voice. Sarris passed away at St. Luke's Hospital on the Upper East Side.
The Times has a great 2009 retrospective on Sarris for those curious.