Blessed with a large, open face and a wide-eyed gaze that communicated gullibility and simple-mindedness, Mr. Poston made a career out of being the endearing/annoying sidekick to smarter characters. Audiences associated him most closely with Newhart. Mr. Poston played Cliff, Bob's intrusive, none-too-bright neighbor on the long-running "Bob Newhart Show" in the 1970s. He also had a regular role on the 1980s sitcom "Newhart," playing ineffective handyman George Utley, one of the various, counter-intuitive Vermonters that bedeviled Newhart's life as a country innkeeper.