Frank Nelson's voice - no substitute

Some actors become so identified with a role to the extent that you cannot visualize them in any other. Percy Kilbride as Pa Kettle and John Banner as Sgt. Schultz are a couple that come to mind. In a similar way, there were certain roles on radio for which there was no acceptable voice except that of Frank Nelson. When he would answer Jack Benny with his "Ye-e-e-e-e-ssss?" it just fit into place. No one else could have done it.

HERE is more about Frank Nelson.