Dennis dagba ni Kenesaw, Nebraska, ati Lincoln Nebraska, ti o jade lati Ile-iwe giga Lincoln High School ni odun 1955; okan ninu awon omo ti won jo wa ni kilaasi je akowe pelu apanilerin-in, Dick Cavett.. 
Oṣere lobinrin naa gba irawọ meji lori Hollywood Walk of Fame ti won si gba wole si awon alawo dudu ti won je osere Hall ti Fame ni odun 1975.. 