Dennis or Denis O'Brien may refer to:Dennis O'Brien, professional ice hockey player in the National Hockey League Dennis M. O'Brien, former speaker, PA House of Representatives, and member, 167th District Denis O'Brien, Irish entrepreneur, charman of Digicel Denis O'Brien (footballer), Australian footballer for Collingwood Denis O'Brien (1899–1942), veteran of the Easter Rising and the Irish Republican Army Denis O'Brien (politician) (1837–1909), New York state attorney general Denis O'Brien (producer) (1941–2021), co-founder of HandMade Films with George Harrison Denis Patrick O'Brien, English economist Denny O'Brien, American columnist, journalist and radio commentator G. Dennis O'Brien, former president of the University of Rochester