Al was a loyal soldier who owed the Corleones big time (DC is right read the back story in the novel) and who paid them back with years of loyalty. As for his being a horrible person, of course he was he was a professional hit man! But that said, all Al ever did was follow orders.
"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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