I think as far as Bit Actors go, Lou Jacobi (1913 - 2009) set a standard. He was consistently good in just about everything he did, or at least in everything I saw him in. IMDb lists 68 acting roles from 1953 until his last film, I.Q. in 1994, a rom-com with Walter Matthau, Meg Ryan and Tim Robbins.
He started out on the stage and continued to work in plays through the years. I saw him once in the 1970's at the old Valley Forge Music Fair. He was also in some big hit movies, The Diary of Anne Frank in 1959 and Irma la Douce in 1963, plus working with Woody Allen, Natalie Wood, Peter Falk, Bette Davis, Peter O'Toole, Dudley Moore and many others.