I thought he was brilliantly cast, mostly for the reasons stated above. Barzini was sort of the bridge of the old school Vito/Tattaglia type dons to what Michael would become. No telling how far Barzini might have gone if he had not had that unfortunate accident on the courthouse steps.
"Io sono stanco, sono imbigliato, and I wan't everyone here to know, there ain't gonna be no trouble from me..Don Corleone..Cicc' a port!"
"I stood in the courtroom like a fool."
"I am Constanza: Lord of the idiots."
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