Although i admit i only know him from two roles, Alfred and Dr. Octopus, Efrem Zimbalist JR. is one of my favorite voice actors for supporting characters and guest-stars.
As Alfred Pennyworth, in Batman The Animated Series, Gotham Knights, and occasionally in Superman and Justice League, he proved himself to be very good acting as the butler. His Alfred, to me, is what I think of while thinking of Alfred. He is, possibly, Alfreds best actor/voice actor. In my opinion, I believe that Alastair Duncan was heavily influenced by him while playing his role as the character in The Batman, and all actors for an animated Alfred in the future will do the same that he did.
As "Doc Ock", in Spider-man tas, from the 90's, he does a great job at pulling off a sinster villain, although not perfect, that made me surprised he was the same who did the voice of Alfred.