O'Brien passed away last Saturday (26Jun10), his son Liam has confirmed.
His decades-long career included memorable roles as a hotel doctor in Woody Allen's movie classic Annie Hall and as a debauched businessman in the Broadway musical comedy Promises, Promises.
He also had recurring television roles as judges on dramas including Law and Order, Ryan's Hope, The Edge of Night and Dark Shadows.
However, O'Brien is perhaps most recognisable as the Shell Answer Man, in television and print ads for the petroleum company.
He last appeared on the big screen in the early 1990s, in Six Degrees of Separation and Quiz Show.
O'Brien was survived by his wife Kate, a daughter, three sons, five grandchildren and four great-grandchildren.